Closed loop MBT timing control using ionization feedback

ABSTRACT

This feature of the present invention comprises a closed loop which uses estimated MBT timing criteria and ignition diagnostics (knock, partial-burn, and misfire) to control engine ignition. When the engine is not knock limited, it operates at its MBT timing. When the engine is knock limited, the engine runs at its inaudible knock limit. When the engine is misfire/partial-burn limited, the engine is maintained at its misfire/partial-burn limit. Three different embodiments of the closed loop MBT timing control architecture are disclosed: a cylinder-by-cylinder control, an average control and a mixed control.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional ApplicationSerial No. 60/423,163, filed Nov. 1, 2002, and 60/467,660, filed May 2,2003, the entire disclosure of these applications being considered partof the disclosure of this application and hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates to engine ignition systems. Moreparticularly, it relates to a method of controlling ignition timing.

[0004] 2. Discussion

[0005] The prior art includes a variety of conventional methods fordetecting and using ionization current in a combustion chamber of aninternal combustion engine. However, each of the various conventionalsystems suffer from a great variety of deficiencies. For example, priorart ionization current detection circuits are generally too slow andgenerate a current signal with low signal-to-noise ratio.

[0006] The individual cylinder air to fuel ratio of an internalcombustion engine varies due to the fact that the intake manifold cannotdistribute airflow into the individual cylinders evenly, even when theglobal air to fuel ratio is maintained at stoich. The difference in airto fuel ratio between individual cylinders affects engine emission, fueleconomy, idle stability, vehicle Noise, Vibration and Handling, etc.

SUMMARY OF THE INVENTION

[0007] In view of the above, the described features of the presentinvention generally relate to one or more improved systems, methodsand/or apparatuses for detecting and/or using an ionization current inthe combustion chamber of an internal combustion engine.

[0008] In one embodiment, the present invention is a method which usesestimated MBT timing criteria and ignition diagnostics to control engineignition timing, wherein the ignition diagnostics comprises knock andmisfire information.

[0009] In another preferred embodiment, the method of controlling engineignition timing further comprises the steps of calculating the MBTtiming criteria, the knock information and the misfire information,generating an MBT error signal by comparing the MBT criteria with a MBTreference signal, outputting the MBT error signal to a proportional andintegral controller, producing a proportional error signal bymultiplying the error signal by a proportional gain, producing anintegrated error signal by integrating the error signal with an integralgain, resetting the integrated error signal if an engine is knock ormisfire limited, outputting a feedforward signal, and outputting atiming signal by summing the proportional error signal, the integratederror signal, and the feedforward signal.

[0010] In a further preferred embodiment, the integrated error signal isreset by a knock limit manager if the engine is knock limited.

[0011] In another preferred embodiment, the integrated error signal isreset by a misfire limit manager if said engine is misfire limited.

[0012] In a further preferred embodiment, the present inventioncomprises a closed loop MBT timing controller, comprising a proportionaland integral controller, a knock limit manager operably connected to theproportional and integral controller a misfire limit manager operablyconnected to the proportional and integral controller, and a saturationmanager operably connected to the proportional and integral controller.

[0013] In another preferred embodiment, the closed loop MBT timingcontroller further comprises a plurality of the knock limit managers,wherein each of the plurality of knock limit managers corresponds to oneof a plurality of cylinders, a plurality of the misfire limit managers,wherein each of the plurality of knock limit managers corresponds to oneof the plurality of cylinders, and a plurality of the proportional andintegral controllers, wherein each of the proportional and integralcontrollers corresponds to one of the plurality of cylinders.

[0014] In a further preferred embodiment, the closed loop MBT timingcontroller comprises a plurality of the knock limit managers, whereineach of the plurality of knock limit managers corresponds to one of aplurality of cylinders, a plurality of the misfire limit managers,wherein each of the plurality of knock limit managers corresponds to oneof the plurality of cylinders, and wherein the proportional and integralcontroller controls all of the cylinders.

[0015] In another preferred embodiment, the closed loop MBT timingcontroller comprises a single proportional and integral controller, asingle knock limit manager, and a single misfire limit manager, andwherein the proportional and integral controller uses a single MBTtiming control parameter, the knock limit manager uses worst case knockinformation and the misfire limit manager uses worst case misfireinformation to control all cylinders globally.

[0016] Further scope of applicability of the present invention willbecome apparent from the following detailed description, claims, anddrawings. However, it should be understood that the detailed descriptionand specific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will become more fully understood from thedetailed description given here below, the appended claims, and theaccompanying drawings in which:

[0018]FIG. 1 illustrates an ionization feedback and control system;

[0019]FIG. 2 is a graph of an ionization signal;

[0020]FIG. 3 is a graph that compares the secondary signals and theionization signals;

[0021]FIG. 4 is a graph of an ionization signal when the plug is fouledand the insulator is overheated;

[0022]FIG. 5 illustrates the effect of pre-ignition on an ionizationsignal;

[0023]FIG. 6 is a diagnostics flowchart of the steps taken in thepresent embodiment of a method of monitoring ignition efficiency;

[0024]FIG. 7 is a flowchart of the steps taken in the present embodimentto diagnose the ignition using the ionization signal;

[0025]FIG. 8 is an electrical schematic of a circuit for measuringionization current in a combustion chamber of an internal combustionengine;

[0026]FIG. 9a is a graph of the control signal V_(IN) from the PCM tothe IGBT versus time.

[0027]FIG. 9b is a graph of the current flow I_(PW) through the primarywinding of the ignition coil versus time;

[0028]FIG. 9c illustrates an output voltage signal Vout resulting from anormal combustion event.

[0029]FIG. 10a is a block diagram of the ignition diagnostics andfeedback control of the present invention;

[0030]FIG. 10b is a block diagram of the ignition diagnostics andfeedback control of the present invention containing the features ofeach subsystem;

[0031]FIG. 11 is a graph of an ionization current signal that ismultiplexed with charge feedback signal;

[0032]FIG. 12 is a drawing of the ignition diagnostics subsystem of thepresent n;

[0033]FIG. 13 is a logic block diagram of the system architecture of theignition ics and feedback control system;

[0034]FIG. 14 illustrates an Air/Fuel ratio sweep vs. crank angle;

[0035]FIG. 15 is a plot of a 300 cycle average ionization at wide openthrottle condition ratio sweep at MBT for Lambda=1.2, 1.1, 1.0, 0.95,0.9, 0.85, 0.8

[0036]FIG. 16 illustrates an A/F ratio sweep at WOT;

[0037]FIG. 17 illustrates a 3000 rpm SA=20 BTDC Air/Fuel ratio sweep atWOT

[0038]FIG. 18 illustrates the A/F ratio perturbation of the presentinvention;

[0039]FIG. 19 illustrates the A/F ratio optimization of the presentinvention;

[0040]FIG. 20 illustrates the real-time WOT A/F ratio optimizationmethod of the invention;

[0041]FIG. 21 is a flowchart of the real-time WOT A/F ratio optimizationmethod of the invention;

[0042]FIG. 22 is a logic block diagram of the real-time WOT A/F ratiooptimization er of the present invention;

[0043]FIG. 23 illustrates the closed loop retard spark control usingionization current feedback apparatus of the present invention;

[0044]FIG. 24 is a flowchart of the steps taken in the presentembodiment in deciding whether to advance or retard the ignition timing;

[0045]FIG. 25a illustrates the closed loop cold start control methodwhen the partial burn index and the misfire index are inactive.

[0046]FIG. 25b illustrates the closed loop cold start control methodwhen the partial burn index is active and the misfire index is inactive.

[0047]FIG. 25c illustrates the closed loop cold start control methodwhen the misfire index is active.

[0048]FIG. 26 is a logic block diagram of the adaptive learning manager.

[0049]FIG. 27 are plots of three cases of ionization waveforms;

[0050]FIG. 28 is a block diagram of the multi-criteria MBT timingestimation method of the present invention;

[0051]FIG. 29 illustrates a logic block diagram of the presentinvention;

[0052]FIG. 30 is a flowchart of the steps taken by the multi-criteriaMBT timing estimation method and apparatus of the present invention;

[0053]FIG. 31 is a logic block diagram of an individual cylinder MBTtiming controller;

[0054]FIG. 32 is a flowchart of steps taken by the PI controller of thepresent invention;

[0055]FIG. 33 is a logic block diagram of the closed loop MBT timing PIcontroller of the present invention;

[0056]FIG. 34 is a logic block diagram of the closed loop knock sparklimit management of the present invention;

[0057]FIG. 35 is a flowchart of the steps taken by the present inventionduring closed loop control when the engine is knock limited;

[0058]FIG. 36 is a logic block diagram of the closed loop retard timinglimit management of the present invention;

[0059]FIG. 37 is a flowchart of the steps taken by the present inventionduring closed loop control when the engine is misfire limited;

[0060]FIG. 38 is a logic block diagram of the average MBT timing controlof the present invention;

[0061]FIG. 39 is a logic block diagram of the mixed MBT timing controlof the present invention;

[0062]FIG. 40 is a plot of the relationship between A/F ratio and MBTspark timing;

[0063]FIG. 41 illustrates the relationship between A/F ratio and MBTspark timing for the individual cylinders of a 2.0 L, four cylinderengine;

[0064]FIG. 42 is a plot of the linear relationship between A/F ratio andMBT timing information for the individual cylinders of a 2.0 L, fourcylinder engine;

[0065]FIG. 43 is a logic block diagram of the closed loop individualcylinder A/F ratio balancing control method of the present invention;

[0066]FIG. 44 is a flowchart of the closed loop individual cylinder A/Fratio balancing control method of the present invention;

[0067]FIG. 45 illustrates the look-up table which comprises feedforwardfuel trim coefficient vectors FT_(FDD);

[0068]FIG. 46 is a logic block diagram of the air to fuel ratio controlsystem of the present invention;

[0069]FIG. 47 is a plot of IMEP COP vs. MBT timing as a function of EGRrate;

[0070]FIG. 48 is a plot of the knock limited EGR rate of the presentinvention;

[0071]FIG. 49 is a logic block diagram of the closed loop EGR ratecontrol of the present invention;

[0072]FIG. 50 is a flowchart of steps taken by the closed loop EGR ratecontroller of the present invention;

[0073]FIG. 51a is a flowchart of steps taken by the logic blocks of FIG.49;

[0074]FIG. 51b is a flowchart of steps taken by the logic blocks of FIG.49;

[0075]FIG. 52 is a graph of mass fraction burned and its first andsecond derivatives;

[0076]FIG. 53 is a graph of net pressure its derivatives versus crankangle;

[0077]FIG. 54 is a graph of torque change with spark timing;

[0078]FIG. 55 is a graph of net pressure acceleration change with sparktiming;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0079] The present invention detects an ionization signal in an enginecombustion chamber from an ionization detection circuit. The system andassociated subsystems described herein use the detected ionizationsignal to monitor ignition parameters, diagnose and improve engineperformance, detect cylinder ID, control air-to-fuel ratio, controlspark retard timing, control minimum timing for best torque timing, andcontrol exhaust gas recirculation, in addtion to other featuresdisclosed in the following embodiments. For clarity, it is noted thatmany of the details concerning the method and apparatus for using thelinear relationship between air to fuel ratio versus minimum timing forbest torque criteria to balance the air to fuel ratio for individualcylinders according to the present invention are described in Section Hof this detailed description.

[0080] This detailed description includes a number of inventive featuresgenerally related to the detection and/or use of an ionization current.The features may be used alone or in combination with other describedfeatures. While one or more of the features are the subject of thepending claims, other features not encompassed by the appended claimsmay be covered by the claims in one or more separate applications filedon even date by or on behalf of the assignee of the present application.

[0081] For clarity, each of the features are described in separatesections of this detailed description. Section A discloses the use of anionization signal from an ionization detection circuit to monitorignition parameters, such as primary charge timing (or time), primarycharge duration, ignition or spark timing, and ignition or sparkduration for future “smart” ignition system control.

[0082] Section B discloses a circuit for measuring ionization current ina combustion chamber of an internal combustion engine in this circuit,the ignition current and the ionization current flow in the samedirection through the secondary winding of the ignition coil and thecircuit detects an ionization signal by applying a bias voltage betweena spark plug gap. Notwithstanding the described preferred circuit, thoseskilled in the art will appreciate that many of the features of theinvention may be implemented through other ionization detection circuitsor methodologies without departing from the scope of the appendedclaims.

[0083] Section C discloses an ignition diagnostics and a feedbackcontrol system based upon detected ionization current in an individualcylinder. The system is divided into two subsystems, the ignitiondiagnostics subsystem and the ignition feedback control subsystem, bothof which function to improve fuel economy and reduce emission enginecalibrations.

[0084] Section D discloses the use of an ionization signal to optimizethe air to fuel ratio of a combustion mixture when an engine is operatedat wide open throttle. The ionization signal is used to detect the airto fuel ratio that yields the highest torque at wide open throttle. Atthe same time, a closed loop controller is used to regulate the air tofuel ratio when the engine is operated at the wide open throttle.

[0085] Section E discloses using a closed loop spark timing controllerto control the spark retard timing during an engine cold start to retardthe engine spark timing as much as possible without engine misfire andwith minimum partial burn. The increased exhaust temperature heats upthe catalyst quickly which, as a result, reduces hydrocarbon emissions.

[0086] Section F discloses a method to determine engine minimum sparktiming for best torque timing at current operational conditions using aspark plug ionization signal. It is a multi-criteria minimum timing forbest torque timing estimation method which utilizes a combination of themaximum flame acceleration location, the 50% burn location, and thesecond peak location to determine engine minimum timing for best torquetiming.

[0087] Section G discloses a subsystem comprising a closed loopcontroller which uses estimated minimum timing for best torque timingcriteria generated from either (or both) an ionization signal and anin-cylinder pressure signal and ignition diagnostics (knock,partial-burn, and misfire) to control engine ignition timing. Threedifferent embodiments of the closed loop minimum timing for best torquetiming control architecture are disclosed. They are differentiated bywhether the minimum timing for best torque timing is controlledcylinder-by-cylinder or globally. The first embodiment controls theengine minimum timing for best torque spark timing of each cylinderindividually. That is, the minimum timing for best torque, knock, andmisfire information of a given cylinder is used to control thatcylinder's minimum timing for best torque timing. The second embodimentuses an averaged approach. The third embodiment uses a mixed approach.

[0088] Section H uses the linear relationship between air to fuel ratioversus minimum timing for best torque criteria to balance the air tofuel ratio for individual cylinders. In a preferred embodiment, a closedloop controller is used to adjust (or trim) the fuel of individualcylinders such that all cylinders have the same minimum timing for besttorque timing criterion.

[0089] Section I uses the ionization signal and closed loop control ofthe exhaust gas re-circulation to provide the engine with either theminimum timing for best torque timing or knock limited timing to yieldthe maximum fuel economy benefits associated with exhaust gasre-circulation.

[0090] Section J uses the maximum acceleration rate of the net pressureincrease resulting form the combustion in a cylinder to control sparktiming.

[0091] Section A: Ignition Diagnosis Using Ionization Signal

[0092] This feature utilizes the ionization signal from an ionizationdetection circuit to monitor ignition parameters, such as primary chargetiming (or time), primary charge duration, ignition or spark timing, andignition or spark duration for future “smart” ignition system control.In addition, the ionization signal is also used to detect spark plugcarbon fouling, insulator overheating, pre-ignition, as well as a failedionization circuit or ignition coil.

[0093] The performance of an engine is heavily dependent upon theperformance of its ignition system, especially at low load and high EGR(exhaust gas recirculation) conditions. Understanding how the ignitionsystem behaves at various engine conditions is very beneficial to“smart” control of the ignition system. Typically, the primary coil ofan ignition system is charged close to a desired amount of energy as afunction of engine operational conditions such as the local mixture A/F(air to fuel) ratio, pressure, temperature, and EGR concentration. Theactual charged energy of the primary coil and discharged energy of thesecondary coil are unknown. This leads to an ignition system that is notrobust to parts-to-parts variation, engine aging, engine operationalenvironmental charges, etc. To improve the ignition system robustness, a“smart” ignition system that can change its charged energy to match thedischarged energy is desirable. Therefore, the secondary dischargeinformation is very important. Since the breakdown voltage and sparkduration at the discharge moment can be different from cycle to cycle,it is desirable to monitor some of these parameters.

[0094] This invention uses the spark plug ionization signal to monitorthe primary charge time (or primary charge timing 146) and primarycharge duration, and also the secondary discharge time and duration tolay the foundation for “smart” control of the ignition system 110. Inaddition, this invention also includes using the ionization signal todetect spark plug malfunction, such as carbon fouling or insulatoroverheating 197, pre-ignition 190, and a failed ionization circuitor/and ignition coil.

[0095] This feature of the invention is generally directed to asubsystem of an ignition diagnostics and feedback control system usingionization current feedback. The relationship of this subsystem to thediagnostics and control system is shown in FIG. 1 in the top box“Ignition system diagnostics”, 140, 150, 146, 160, 170, and 197, whichcomprises the following ignition parameters: ignition duration 170,charge duration 150, warning signal 197, primary charge time 146,ignition timing 160, and pre-charge 140. The four blocks of the ignitiondiagnostics and feedback control system using ionization currentfeedback that are directed to spark timing 1480 are the CL knock(advance) limit control 1450, the closed-loop MBT spark control 1430,1490 and 1495, CL misfire & partial burn (retard) limit control 1460 andthe CL cold start retard limit control 1000. There are two blocksdirected to the fuel trim vector 975, the individual cylinder A/F ratiocontrol 1300 and the WOT A/F ratio optimization 1900. There is one blockdirected to the desired EGR rate 1630, the EGR rate optimization 1600.The three other blocks shown in FIG. 1 are an analog signal processingblock ASP, an A/D conversion block A/D and a parameter estimation block1800. The parameter estimation block is shown outputting knock 1404, MBT1435 and misfire 1414 signals. The input to the analog signal processingblock ASP is an ionization current 100.

[0096] A typical ionization signal 100 versus crank angle is shown inFIG. 2. Note that the signal shown is a voltage that is proportional tothe detected ionization current. Comparing the secondary voltage 120 andcurrent waveforms 130 (FIG. 3), it is clear that the initial rise of theion signal before the sharp change at the ignition time is thepre-charge (or start of charge) of the primary coil 140. See FIG. 2.After the primary coil charge is completed, the signal goes down andrises almost vertically (i.e., a step rise) versus crank angle. Thebreakdown has occurred at the step's rising edge. Spark timing can bedetected based on this point. That is, the ignition or spark time occurswhen the ionization signal has a step rise. This is the ignition orspark time 160. The time difference between the first rise and thestepped rise is the primary charge duration 150. When the arc betweenthe spark gap dies out, the signal declines rapidly and the secondarycurrent 130 due to the spark reaches zero (see FIG. 3). The durationbetween the sharp stepped rising and the subsequent declining representsthe ignition duration 170. Therefore, based on the ionization signal,the primary charge time 146, the primary charge duration 150, theignition timing 160, and the ignition duration 170 can be detected.These parameters can be monitored for every cylinder of the engine foreach engine cycle.

[0097] When a spark plug is fouled, or the spark plug insulator isoverheated, or the plug itself is temporarily contaminated by fuelspray, the insulator of the spark plug serves as a conductor. At theseconditions, the ionization signal baseline is no longer equal to thebias voltage 105. Depending on how badly the plug is fouled and howoverheated the insulator is, the ionization baseline will be elevated180 (FIG. 4) from the bias voltage 105. Meanwhile, part of the ignitionenergy will leak through the fouled plug or the insulator during theprimary charge period. Eventually the remaining energy is not enough tojump the spark gap and a misfire will occur (196) (FIG. 6). For somecases, the baseline can be so high that it reaches the limit of theionization signal and the signal becomes of little use. Once thebaseline is elevated to (or beyond) a certain threshold (e.g., anelevation of approximately 20% or 1 volt above the initial baseline), awarning signal indicating plug fouling or overheating will be sent out197 (FIG. 6).

[0098] When pre-ignition occurs in the cylinder, the ionization signal100 will detect ions before the ignition happens (190), see FIG. 5 whichshows pre-ionization due to pre-ignition. One pre-ignition cycle couldlead to an even earlier pre-ignition during the next cycle and damagethe engine. It is desirable to control the engine to a cooler operatingcondition once the pre-ignition is detected.

[0099] In order to detect an open or a shorted ionization circuit, thebias voltage (105) is sampled far away from the ignition and combustionevents (e.g., 180 degree after the top dead center). If the sampled biasvoltage is below a given threshold (such as 0.5 volt), an openionization circuit or a short to ground fault can be detected 198 (FIG.6); if the bias voltage is greater than a threshold (e.g., 4.5 volts),an ionization circuit that is shorted to the battery shall be declared199 (FIG. 6). The open or short circuit information can then be used todiagnose the condition of the ignition system (see FIGS. 6 and 7).

[0100] Section B: Circuit for Measuring Ionization Current

[0101]FIG. 8 is a basic electrical schematic of a circuit 10 formeasuring ionization current in a combustion chamber of an internalcombustion engine. The components and configuration of the circuit 10are described first, followed by a description of the circuit operation.

[0102] First, with regard to the components and configuration of thisfeature, the circuit 10 includes an ignition coil 12 and an ignition ora spark plug 14 disposed in a combustion chamber of an internalcombustion engine. The ignition coil 12 includes a primary winding 16and a secondary winding 18. The ignition plug 14 is connected inelectrical series between a first end of the secondary winding 18 andground potential. The electrical connections to a second end of thesecondary winding 18 are described further below. A first end of theprimary winding 16 is electrically connected to a positive electrode ofa battery 20. A second end of the primary winding 16 is electricallyconnected to the collector terminal of an insulated gate bipolartransistor (IGBT) or other type of transistor or switch 22 and a firstend of a first resistor 24. The base terminal of the IGBT 22 receives acontrol signal, labeled V_(IN) in FIG. 8, from a powertrain controlmodule (PCM) not shown. Control signal V_(IN) gates IGBT 22 on and off.A second resistor 25 is electrically connected in series between theemitter terminal of the IGBT 22 and ground. A second end of the firstresistor 24 is electrically connected to the anode of a first diode 26.

[0103] The circuit 10 further includes a capacitor 28. A first end ofthe capacitor 28 is electrically connected to the cathode of the firstdiode 26 and a current mirror circuit 30. A second end of the capacitor28 is grounded. A first zener diode 32 is electrically connected acrossor, in other words, in parallel with the capacitor 28 with the cathodeof the first zener diode 32 electrically connected to the first end ofthe capacitor 28 and the anode of the first zener diode 32 electricallyconnected to ground.

[0104] The current mirror circuit 30 includes first and second pnptransistors 34 and 36 respectively. The pnp transistors 34 and 36 arematched transistors. The emitter terminals of the pnp transistors 34 and36 are electrically connected to the first end of the capacitor 28. Thebase terminals of the pnp transistors 34 and 36 are electricallyconnected to each other as well as a first node 38. The collectorterminal of the first pnp transistor 34 is also electrically connectedto the first node 38, whereby the collector terminal and the baseterminal of the first pnp transistor 34 are shorted. Thus, the first pnptransistor 34 functions as a diode. A third resistor 40 is electricallyconnected in series between the collector terminal of the second pnptransistor 36 and ground.

[0105] A second diode 42 is also included in the circuit 10. The cathodeof the second diode 42 is electrically connected to the first end of thecapacitor 28 and the emitter terminals of the first and second pnptransistors 34 and 36. The anode of the second diode 42 is electricallyconnected to the first node 38.

[0106] The circuit 10 also includes a fourth resistor 44. A first end ofthe fourth resistor 44 is electrically connected to the first node 38. Asecond end of the fourth resistor 44 is electrically connected thesecond end of the secondary winding 18 (opposite the ignition plug 14)and the cathode of a second zener diode 46. The anode of the secondzener diode 46 is grounded.

[0107] Referring now to FIGS. 8 and 9, the operation of the circuit 10is described. FIG. 9a is a graph of the control signal V_(IN) from thePCM to the IGBT 22 versus time. FIG. 9b is a graph of the current flowI_(PW) through the primary winding 16 of the ignition coil 12 versustime. FIG. 9c is a graph of an output voltage signal from the circuit 10versus time. As mentioned above, the IGBT 22 receives the control signalV_(IN) from the PCM to control the timing of 1) the ignition orcombustion and 2) the charging of the capacitor 28. In this circuitconfiguration, the IGBT 22 is operated as a switch having an OFF, ornon-conducting state, and an ON, or conducting state.

[0108] Initially, at time=t₀, the capacitor 28 is not fully charged. Thecontrol signal V_(IN) from the PCM is LOW (see FIG. 9a) therebyoperating the IGBT 22 in the OFF, or non-conducting, state. Primarywinding 16 sees an open circuit and, thus, no current flows through thewinding 16.

[0109] At time=t₁, the control signal V_(IN) from the PCM switches fromLOW to HIGH (see FIG. 9a) thereby operating the IGBT 22 in the ON, orconducting, state. Current from the battery 20 begins to flow throughthe primary winding 16 of the ignition coil 12, the conducting IGBT 22,and the second resistor 25 to ground. Any of a number of switches orswitching mechanisms can be used to connect current through the primarywinding 16. In a preferred embodiment IGBT 22 is used. Between time=t₁and time=t₂, the primary winding current I_(PW) (illustrated in FIG. 8with a dotted line) begins to rise. The time period between time=t₁ andtime=t₂ is approximately one millisecond which varies with the type ofignition coil used.

[0110] At time=t₂, the control signal V_(IN) from the PCM switches fromHIGH to LOW (see FIG. 9a) thereby operating the IGBT 22 in the OFF, ornon-conducting, state. As the IGBT 22 is switched OFF, flyback voltagefrom the primary winding 16 of the ignition coil 12 begins to quicklycharge the capacitor 28 up to the required bias voltage. Between time=t₂and time=t₃, the voltage at the first end of the secondary winding 18connected to the spark plug 14 rises to the voltage level at which theignition begins. The time period between time=t₂ and time=t₃ isapproximately ten microseconds. The first resistor 24 is used to limitthe charge current to the capacitor 28. The resistance value of thefirst resistor 24 is selected to ensure that the capacitor 28 is fullycharged when the flyback voltage is greater that the zener diode.

[0111] At time=t₃, an ignition voltage from the secondary winding 18 ofthe ignition coil 12 is applied to the ignition plug 14 and ignitionbegins. Between time=t₃ and time=t₄, combustion of the air/fuel mixturebegins and an ignition current I_(IGN) (illustrated in FIG. 8 with adash-dot line) flows through the second Zener diode 46, the secondarywinding 18 of the ignition coil 12, and the ignition plug 14 to ground.At time=t₄, the ignition is completed and the combustion of the air/fuelmixture continues.

[0112] At time=t₅, the combustion process continues and the chargedcapacitor 28 applies a bias voltage across the electrodes of theignition plug 14 producing an ionization current I_(ION) due to the ionsproduced by the combustion process which flows from the capacitor 28.The current mirror circuit 30 produces an isolated mirror currentI_(MIRROR) identical to the ionization current I_(ION). A bias currentI_(BIAS) (illustrated in FIG. 8 with a phantom or long dash-shortdash-short dash line) which flows from the capacitor 28 to the secondnode 48 is equal to the sum of the ionization current I_(ION) and theisolated mirror current I_(MIRROR) (i.e., I_(BIAS)=I_(ION)+I_(MIRROR)).

[0113] The ionization current I_(ION) (illustrated in FIG. 8 with adashed line) flows from the second node 48 through the first pnptransistor 34, the first node 38, the fourth resistor 44, the secondarywinding 18 of the ignition coil 12, and the ignition plug 14 to ground.In this manner, the charged capacitor 28 is used as a power source toapply a bias voltage, of approximately 80 volts, across the spark plug14 to generate the ionization current I_(ION). The bias voltage isapplied to the spark plug 14 through the secondary winding 18 and thefourth resistor 44. The secondary winding induction, the fourth resistor44, and the effective capacitance of the ignition coil limit theionization current bandwidth. Accordingly, the resistance value of thefourth resistor 44 is selected to maximize ionization signal bandwidth,optimize the frequency response, and also limit the ionization current.In one embodiment of the present invention, the fourth resistor 44 has aresistance value of 330 k ohms resulting in an ionization currentbandwidth of up to twenty kilohertz.

[0114] The current mirror circuit 30 is used to isolate the detectedionization current I_(ION) and the output circuit. The isolated mirrorcurrent I_(MIRROR) (illustrated in FIG. 8 with a dash-dot-dot line) isequal to or, in other words, a mirror of the ionization current I_(ION).The isolated mirror current I_(MIRROR) flows from the second node 48through the second pnp transistor 36 and the third resistor 40 toground. To produce a isolated mirror current signal IMIRROR which isidentically proportional to the ionization current I_(ION), the firstand second pnp transistors 34 and 36 must be matched, i.e., have theidentical electronic characteristics. One way to achieve such identicalcharacteristics is to use two transistors residing on the same piece ofsilicon. The isolated mirror current signal I_(MIRROR) is typically lessthan 300 microamps. The third resistor 40 converts the isolated mirrorcurrent signal I_(MIRROR) into a corresponding output voltage signalwhich is labeled as V_(OUT) in FIG. 8. The resistance value of the thirdresistor 40 is selected to adjust the magnitude of the output voltagesignal V_(OUT). The second diode 42 protects the mirror transistors 34and 36 by biasing on and providing a path to ground if the voltage atnode 38 crosses a threshold. A third transistor can also be used toprotect the mirror transistor.

[0115]FIG. 9c illustrates an output voltage signal V_(OUT) resultingfrom a normal combustion event. The portion of the output voltage signalV_(OUT) from time=t₅ and beyond can be used as diagnostic informationregarding combustion performance. To determine the combustionperformance for the entire engine, the ionization current in one or morecombustion chambers of the engine can be measured by one or morecircuits 10 respectively.

[0116] In the present circuit 10, the ignition current I_(IGN) and theionization current I_(ION) flow in the same direction through thesecondary winding 18 of the ignition coil 12. As a result, theinitiation or, in other words, the flow of the ionization current aswell as the detection of the ionization current is quick. In the presentcircuit 10, the charged capacitor 28 operates as a power source. Thus,the circuit 10 is passive or, in other words, does not require adedicated power source. The charged capacitor 28 provides a relativelyhigh bias voltage from both ionization detection and the current mirrorcircuit 30. As a result, the magnitude of the mirrored, isolated currentsignal I_(MIRROR) is large and, thus, the signal-to-noise ratio is high.

[0117] Section C: Ignition Diagnosis and Combustion Feedback ControlSystem Using an Ionization Signal

[0118] The spark ignition (SI) engine combustion process is governed bythe in-cylinder air to fuel (A/F) ratio, temperature and pressure,exhaust gas re-circulation (EGR) rate, ignition time and duration, andother factors. Engine emission and fuel economy are dependent on theengine's combustion process. For homogeneous combustion engines, mostoften the engine air to fuel (A/F) ratio is controlled in a closed loopusing a feedback signal either from a heated exhaust gas oxygen (HEGO)or from a universal exhaust gas oxygen (UEGO) sensor. The exhaust gasre-circulation (EGR) rate is controlled with the help of a delta (A)pressure measurement. Due to the high cost of an in-cylinder pressuresensor, engine spark timing is controlled in an open loop and iscorrected using a knock detection result. As a result of open loopcontrol, the engine combustion process is sensitive to operationalconditions, engine-to-engine variation, engine aging, and other relatedfactors. This sensitivity results in a complicated calibration processdue to engine mapping and the calibration process of various sparktiming lookup tables, trims and adders, where the spark timing tablesare used to vary the ignition/spark timing as function of engine speedand load, and the trims and adders are used to compensate engineignition/spark timing when a special engine operational condition occurs(e.g., transient operation). The present invention proposes an ignitiondiagnostics and feedback control system using an ionization current as afeedback signal to improve ignition system robustness with respect toengine operational conditions, engine-to-engine variations, engineaging, and other related factors to reduce engine calibration needs.

[0119] Spark ignited engine systems in the prior art have the severaldisadvantages and drawbacks. For example, the ignition control processis open loop and the actual ignition time and duration are unknown.Further, the command ignition time is controlled in an open loop withlookup tables as function of engine speed, load, etc., along with trimsand adders to compensate engine operational condition variations.Additionally, the limitations imposed by using accelerometer-basedengine knock detection prevent the spark ignition engine from running atits knock limit when needed, leading to reduced fuel economy.

[0120] In contrast, features of the present invention include individualcylinder diagnostics features such as ignition system diagnostics:charge timing 146, charge duration 145, ignition timing 160, ignitionduration 170, plug fouling 197, pre-ignition 190, etc.; misfiredetection: misfire flag 414, partial burn flag 412, and other relatedfactors; knock detection: knock flag 404 and knock intensity 402; andMBT timing detection: robust multi-criteria MBT timing estimator 200.

[0121] Furthermore, features of the present invention also includecontrol features such as closed loop cold start retard spark controlusing ionization feedback 1000; Closed loop MBT timing control usingionization feedback 1430, 1490, 1495; Closed-loop individual cylinderA/F ratio balancing 1300; Optimal wide open throttle air/fuel ratiocontrol 1900; and Exhaust gas control using a spark plug ionizationsignal 1600.

[0122] The present invention includes an ignition diagnostics and afeedback control system based upon detected ionization current in anindividual cylinder 801. The system 801 is divided into two subsystemsas illustrated in FIGS. 10a and 10 b. The ignition diagnostics subsystem802 and the ignition feedback control subsystem 803 both function toimprove fuel economy and reduce emission engine calibrations.

[0123] A typical ionization signal is plotted in FIG. 11 which showsthat the detected ion current signal 100 can be divided into twosections, charge ignition 141 and post-charge ignition signals 143.

[0124] The architecture of ignition diagnostics subsystem 802 is shownin FIG. 12 and includes four main features. First, the ignition systemdiagnostics provides the ignition primary coil charge timing 146, chargeduration 145, secondary coil discharge timing (or in other words,ignition/spark timing 160), ignition duration 170, fault ignition system(such as failed coil, failed spark plug, etc.) using the charge-ignitionportion 141 of the ion current signal 100. Also, the post ignitionionization current signal 143 is used to detect spark plug fouling 197.

[0125] Second, the misfire detection feature provides individualcylinder misfire information 1410 such as misfire and partial burnconditions using the post ignition ionization current signal 143 and theresults of ignition system diagnostics. The resulting misfire detectionis much more accurate than existing engine speed based misfire detectionsystems, especially at the engine deceleration condition where currentdetection systems fail to provide an accurate detection of misfire. Theexisting speed based misfire detection systems also have difficulty indetecting misfire for those engines with more than eight cylinders.

[0126] Third, the knock detection feature provides knock intensity 1402and knock flag 1404 signals based upon a band-path filteredpost-ignition portion of the ionization signal 100. One advantage ofusing an ionization signal 100 for knock detection is that it enablesindividual cylinder knock detection and also produces a cleaner knocksignal when compared to current accelerometer based knock detectiontechniques which require intensive calibration due to engine valvenoises.

[0127] Fourth, the robust multi-criteria MBT (Minimum timing for BestTorque) timing estimation apparatus and method 200 provides a compoundindex based upon the post-ignition ionization current signal 143 for anindividual cylinder. This index combines multiple MBT timing indexeswhich are calculated using information provided by the ionizationcurrent signal 100 for the 10% mass fraction burned, the 50% massfraction burn, and the peak cylinder pressure (PCP) locations forimproved estimation robustness. When the engine is not knock limited,the index can be used for closed loop control of engine ignition/sparktiming for improved fuel economy, reduced emissions, reducedcalibration, etc.

[0128] The system architecture of the ionization feedback controlsubsystem 803 is shown in FIG. 13 and includes four controllers: (1) aclosed loop cold start retard spark control using ionization feedback1000; (2) a closed loop MBT timing control using ionization feedback1430, 1490, 1495; (3) a closed-loop individual cylinder air to fuelratio balancing control system 1300; and (4) optimal wide open throttleair/fuel ratio control 1900; and (5) exhaust gas control using a sparkplug ionization signal 1600.

[0129] As to the closed loop cold start retard spark control usingionization feedback 1000, it is noted that 70% of the HC emission duringan FTP cycle is produced during a cold start since the catalysttemperature does not reach its operational point quickly. Variousapproaches have been developed in the prior art to heat up the catalystquickly during the cold start. One technique involves retarding thespark timing significantly to raise the exhaust temperature so that thecatalyst can be heated up quickly. However, since retarding the sparktiming is limited by partial burn and misfire, open loop calibration ofretard spark timing for a cold start is done very conservatively due toengine-to-engine variations, engine aging, operational conditionvariations, etc. Under closed loop control of retard spark timing of thepresent invention, the engine retard timing limit is adjusted during acold start to reduce the conservativeness and light up the catalyst morequickly, thereby reducing HC emissions during a cold start.

[0130] As to the closed loop MBT timing control using ionizationfeedback 1430, 1490, 1495, when the spark timing of an internalcombustion engine is neither knock limited, nor misfire/partial-burnlimited, the engine operates at its MBT spark timing for best fueleconomy when emission is satisfactory. Existing MBT timing controldisclosed in the prior art is controlled in an open loop based uponengine mapping data. This approach does not compensate forengine-to-engine variations, engine operational conditions, aging ofcomponents, and other related factors. Consequently, many ignition/sparktiming corrections used to compensate for those various conditions,called adders or trims, have to be added for improved engineperformance. The closed loop MBT spark timing control strategy of thepresent invention adjusts the engine spark timing when the engine 161 isneither knock or misfire limited to provide improved fuel economy. Whenthe engine 161 is knock limited, the closed loop control of the presentinvention adjusts the engine ignition/spark timing so that the engine161 runs at its knock limit, thereby providing improved fuel economy andhigh torque output.

[0131] The third controller is the closed-loop individual cylinder airto fuel ratio balancing control system 1300. In the prior art, theairflow passage of an intake manifold for each individual cylinder isquite different. Consequently, the charge air volume and flow patternfor each individual cylinder is different, even at steady stateoperating conditions. Thus, even if the mean air to fuel (A/F) ratio ofall cylinders remains at stoich, the air to fuel ratio of eachindividual cylinder can differ from stoich. In the present invention,the fuel injected for each individual cylinder is adjusted to ensurethat each cylinder has the same air to fuel (A/F) ratio. The proposedindividual cylinder air to fuel (A/F) ratio balancing method andapparatus of the present invention utilizes MBT timing estimationobtained during closed loop MBT timing control to adjust/trim the fuelmetered for each cylinder using a fuel multiplier for each individualcylinder. In addition, a closed loop controller using a HEGO or UEGOsensor keeps the mean air to fuel (A/F) ratio at stoich. By using thefact that the MBT spark timing of a rich cylinder is relatively retardedcompared to one at a stoich air to fuel (A/F) ratio and the MBT sparktiming of a lean cylinder is relatively advanced compared to a stoichone, the individual cylinder fuel multiplier can be modified based upondetected MBT timing index or the resulting MBT timing control to balancerelative air to fuel (A/F) ratios between individual cylinders.

[0132] As noted above, the fourth controller is the optimal wide openthrottle air/fuel ratio control 1900. Normally, the air to fuel (A/F)ratio at wide open throttle (WOT) is adjusted to maximize the enginetorque output. At this point, the engine 161 is operated at its minimumadvanced MBT timing. In the prior art, air to fuel (A/F) ratio at WOT isoptimized using an open loop calibration approach based on enginemapping data. The apparatus and method of the present invention adjuststhe air to fuel (A/F) ratio to minimize MBT spark advance when theengine 161 is running at WOT.

[0133] Finally, with the exhaust gas control using a spark plugionization signal 1600, an ionization signal 100 is used to calculate acombustion stability index. The combustion stability index can be thecombustion burn rate or a parameter related to burn duration. Thecombustion stability index is then used to control the exhaust gasre-circulation (EGR) rate to increase the exhaust gas re-circulation EGRdilution. The EGR rate is increased when the combustion stability indexis below a threshold. This enables the engine to run at an increased EGRrate while maintaining stable combustion. As a result, fuel economy isimproved, while emissions are decreased.

[0134] Section D: Optimal Wide Open Throttle Air/Fuel Ratio Control

[0135] This feature of the present invention uses an ionization signalto optimize the air to fuel ratio (AFR) of a combustion mixture when anengine is operated at wide open throttle (WOT). This yields the highestBMEP (Brake specific Mean Effective Pressure), or in other words,maximizes the engine's torque output with the best fuel economy. Inaddition, spark timing is also optimized.

[0136] Engines are typically operated at a stoichiometric air to fuelratio AFR (which is approximately 14.7 to 1 for gasoline) to optimizecatalytic converter performance. Operating an engine at belowstoichiometric (less than 14.7 to 1) results in operating the enginewith a rich air to fuel ratio AFR. In this instance, the fuel does notcompletely combust and the catalytic converter can get clogged from theresulting emissions. On the other hand, operating an engine at abovestoichiometric (greater than 14.7 to 1) results in operating the enginewith a lean air to fuel ratio AFR. In this instance, there is excessoxygen in the emissions. This causes the catalytic converter to operateat an elevated temperature, thereby limiting the conversion ofnitrogen-oxygen compounds (“NOx”). More importantly, operating at thiscondition for long durations may damage the catalyst converter.

[0137] Normally, oxygen sensors are used when controlling an air to fuelratio AFR. The oxygen sensor measures the presence of oxygen in theair/fuel mixture. However, when operating an engine at wide openthrottle WOT, the air/fuel mixture is outside the stoichiometric range,normally below the stoich. The air to fuel ratio AFR and the sparktiming for engines running at wide open throttle WOT conditions useextensive calibration to produce the best torque output. Due to thenon-stoich operation at wide open throttle WOT, the oxygen sensor (whichgenerates either a rich or a lean signal) can not be used as anindicator of air to fuel ratio AFR. Therefore, the air to fuel ratio AFRis not being controlled in a closed loop under wide open throttleoperation conditions.

[0138] The present invention 900 uses the ionization signal to detectthe air to fuel ratio AFR that yields the highest torque or BMEP at wideopen throttle WOT. At the same time, a closed loop controller is used toregulate the air to fuel ratio AFR when the engine is operated at thewide open throttle WOT. In addition, the engine spark timing isoptimized at its minimum timing for the best torque (MBT) timing for thecorresponding conditions.

[0139] Optimal WOT A/F ratio detection involves optimizing the A/F ratioat wide open throttle WOT condition. When an engine is operating at wideopen throttle WOT condition, it is desired that the engine outputs thehighest BMEP (torque) to meet the torque demand. The highest BMEP ateach engine operating condition is not only a function of the sparktiming, but also a function of the air to fuel ratio AFR if the air tofuel ratio AFR is allowed to deviate from the stoich air to fuel ratio.When an appropriate spark timing is found for the operating condition,the highest BMEP is established through the most efficient combustion.The best combustion efficiency can be achieved when the combustiblemixture attains its fastest laminar flame speed. For most fuels, thefastest laminar flame speed usually occurs at an equivalence ratio φequal to 1.1 (where λ, defined as the inverse of φ, equals to 0.9). Theexcess-air factor, λ, is a factor which indicates the amount that an airto fuel ratio AFR is above or below a stoichiometric mixture. Thus, atλ=1.0, the air/fuel mixture is at stoichiometric. At λ=1.3, the air/fuelmixture is 130% of stoichiometric or 30% above stoichiometric.

[0140] Because an oxygen sensor (which provides either a rich or a leanswitch signal) is of minimal use when trying to sense the air to fuelratio AFR far away from the stoichiometric mixture, existing technologyuses an open loop control strategy and extensive calibration work whenan engine operates at wide open throttle WOT conditions. A sensor thatcan detect an efficient combustion condition is needed to control theair to fuel ratio AFR at wide open throttle WOT conditions in a closedloop.

[0141]FIG. 11 is a typical ionization signal 100 detected from a sparkplug 105 inside the combustion chamber. It is a plot of the ionizationsignal 100 during both charge ignition 141 and post charge ignition 143.After the spark breakdown, a flame kernel is formed in the spark gap.The first peak 162 of the ionization signal 100 is produced as a resultof the initial flame formation. The chemical reaction caused by theflame formation increases the number of ions present in the enginecylinder. After the flame kernel is well established, the flame frontgradually propagates away from the gap and the ionization signal 100gradually declines. Meanwhile, the flame front pushes both unburned andburned gases in front of it and behind it and causes the localtemperature in the vicinity of the gap to increase along with thecylinder pressure. Since the mixture around the spark gap is the firstpart of the mixture burned in the cylinder and is the first part of theburned mixture that is compressed in the cylinder, the local temperatureof the air/fuel mixture is always highest in the gap. As the flamepropagates away, the ionization signal 100 starts to increase again dueto the elevated temperature. When the cylinder pressure reaches itspeak, the gap temperature also reaches its hottest point. Therefore, thesecond peak 166 of the ionization signal 100 occurs as a result of thesecondary ionization due to the high temperature.

[0142] U.S. Pat. No. 6,029,627 discloses that the first peak 162 reachesits highest value when the excess-air factor λ is between 0.9 and 0.95.In addition, the second peak 166 reaches its highest value when λ isaround 1.1. At a light load condition, the first peak 162 most likelypeaks around λ=0.9 as shown in FIG. 14. However, when the engine loadgets higher, the first peak 162 increases as λ increases beyond 0.9. Theincrease in the first peak 162 is due to increased carbon speciesdissociation caused by higher temperatures due to the increased loadcondition. In addition, the second peak 166 does not usually peak aroundλ=1.1 as described in U.S. Pat. No. 6,029,627, but instead occurs aroundλ=0.9.

[0143] Around λ=0.9, both flame speed and flame temperature are at theirhighest. The fastest flame speed indicates the most efficient combustionprocess. The appearance and placement of the second peak 166 depends ondifferent loads, sparks and air to fuel ratios and might not appear atall at some operating conditions. However, at wide open throttle WOTconditions, the second peak 166 will always show up when the mixture isricher than stoichiometric AFR.

[0144] Maximizing either the valley value 164 or the second peak value166 versus the air to fuel ratio AFR can be used as a criterion to findthe most vigorous combustion condition. This condition usually occurswhen λ is between 0.9 and 0.925. From FIG. 15 and FIG. 17, it is clearthat this criterion holds true when minimum timing for the best torqueMBT timing is used for each air to fuel ratio AFR condition. In FIG. 17,the second peak 166 is about 2.6 volts when λ is between 0.9 and 0.925and the valley 164 is about 1.3 volts. Both the second peak 166 and thevalley 164 are at maximum values. This criterion also holds true when afixed spark timing is used for 1500 rpm wide open throttle WOT conditionand 2000 rpm wide open throttle WOT condition as shown in FIG. 14 andFIG. 16 respectively.

[0145] To improve the robustness of the optimal air to fuel ratio AFRdetection capability, the values for the valley 164 and the 2^(nd) peak166 are combined to estimate the optimal air to fuel ratio AFR duringthe wide open throttle WOT operation.

C _(AFR)=(V _(valley) +V _(2nd-PEAK))/2,  (Equation 1).

[0146] V_(valley)+V_(2nd-PEAK) is plotted in FIG. 17. It reaches amaximum around λ=0.9.

[0147] Real-time optimal A/F ratio control algorithm: Note that the airto fuel ratio AFR index C_(AFR) for a specific air to fuel ratio AFRdoes not provide information whether the air to fuel ratio AFR, that theengine is operated at, is optimal or not. A completed relationship ofC_(AFR) and air to fuel ratio AFR is used to determine the preferred airto fuel ratio AFR at wide open throttle WOT operation. However, thisrelationship is a function of many factors, such as engine-to-enginevariation, engine aging, and engine operational conditions (altitude,humility, etc.). Consequently, it is difficult to optimize air to fuelratio AFR for wide open throttle WOT conditions using off-lineoptimization.

[0148] This feature of the present invention optimizes the wide openthrottle WOT air to fuel ratio AFR on-line using the relationshipbetween C_(AFR) and air to fuel ratio AFR at WOT. Similar to a closedloop stoich air to fuel ratio AFR control system, an air to fuel ratioAFR perturbation (or offset) is added to the desired mean air to fuelratio AFR. See FIG. 18 where Δ_(AFR) and T_(P) are the magnitude andperiod of the air to fuel ratio AFR perturbation or air to fuel ratioAFR offset, respectively. The typical value of the perturbationmagnitude Δ_(AFR) is 0.05, and the typical perturbation period isbetween a quarter second and half a second with a 50 percent duty cycle.An optimal WOT air to fuel ratio AFR control gradient parameter can bedefined as:

P _(AFR)=(C _(A/F)(H)−C _(A/F)(L))/Δ_(AFR)  (Equation 2)

[0149] where air to fuel ratio AFR index C_(AFR)(H) corresponds to themaximum A/F ratio index obtained when the air to fuel ratio AFR isperturbed by adding Δ_(AFR), and C_(AFR)(L) corresponds to the minimumair to fuel ratio AFR index obtained when the air to fuel ratio AFR isperturbed by subtracting Δ_(AFR). For a typical case that the nominal λis 0.925 with Δ_(AFR) equal to 0.05 when the engine is running at 3000rpm with wide open throttle, C_(A/F)(H) is 1.85 and C_(A/F)(L) 1.95.Since the air to fuel ratio AFR index C_(AFR) is a convex function ofthe air to fuel ratio AFR (see both FIGS. 16 and 17), there are threepossible ratio gradients for P_(AFR) (see FIG. 19):

[0150] P_(AFR)>0: The engine overall air to fuel ratio AFR with respectto optimal AFR at WOT is rich;

[0151] P_(AFR)=0: The engine overall air to fuel ratio AFR is optimizedfor best torque; and

[0152] P_(AFR)<0: The engine overall air to fuel ratio AFR with respectto optimal AFR at WOT is lean.

[0153] In a preferred embodiment, the real-time control strategy adjuststhe engine air to fuel ratio AFR based upon the air to fuel ratio AFRgradient parameter. During the wide open throttle WOT operation, theengine desired mean excess-air correction factor Δλ is updated using:

Δλ_(DESIRED)(k+1)=Δλ_(DESIRED)(k)+α*P _(AFR)  (Equation 3),

[0154] where α>0 is a calibratable constant coefficient for thereal-time optimization algorithm. In this case, when the P_(AFR) isgreater than 0 (air to fuel ratio AFR is rich), a positive correction(αP_(AFR)>0) is added to the desired mean excess-air correction factor(Δλ_(DESIRED)) by reducing the desired fuel quantity to increase theengine mean A/F ratio, thereby increasing the percentage of air. WhenP_(AFR) is less than 0 (air to fuel ratio AFR is lean), a negativecorrection (αP_(AFR)<0) is added to decrease the desired mean excess-aircorrection factor Δλ, thereby increasing the desired fuel quantity anddecreasing the percentage of air. When P_(AFR) is equal to 0, noadjustment is required.

[0155]FIG. 20 is a diagram of the WOT air to fuel ratio AFR controlmethod discussed above. Each step is number coded and the details aredescribed below. In step 910 the valley and 2^(nd) peak values arefound. More particularly, the valley value 164 and the 2^(nd) peak value166 is calculated using the ionization signal as discussed in “OptimalWOT A/F ratio detection,” where the definition of the valley 164 and the2^(nd) peak 166 are found in FIGS. 14 and 16. This step is updated everyfiring event.

[0156] In step 920, C_(AFR)(H) and C_(AFR)(L) are calculated usingequation 1. As described in FIG. 18, a positive or negative perturbationis added to the desired mean excess-air correction factor Δλ. When thepositive perturbation is added, C_(AFR)(H) is calculated, and when thenegative perturbation is added, C_(AFR)(L) is calculated. The meanvalues of C_(AFR)(H) and C_(AFR)(L) of a perturbation period are used asoutput of this step. Therefore, this step runs every firing event, butoutput every perturbation period (T_(P)). For port injection engines,due to fuel transport delay, the calculation will be delayed until thetransition is completed.

[0157] In step 930, the air to fuel ratio AFR control gradient P_(AFR)is calculated. This step runs every air to fuel ratio AFR perturbationcycle. In order to make sure that the WOT air to fuel ratio AFR isoptimized at a given engine speed, this step calculates P_(AFR) when theengine speed variation is within a calibratable value.

[0158] In step 940, the updated desired air to fuel ratio correctionfactor Δλ_(DESIRED)(k+1) is calculated using Equation 2. This step runsevery air to fuel ratio AFR perturbation period. In the cases when theP_(AFR) is not calculated due to larger engine speed variation,Δλ_(DESIRED)(k+1) shall be set to zero.

[0159] In step 950 the feedforward air to fuel ratio λ_(FFD) iscalculated. The feedforward air to fuel ratio AFR is based upon a lookuptable that is a function of engine speed 135 and other factors. Thistable provides an open loop desired air to fuel ratio AFR for the enginesystem. Normally, this table is obtained through the engine calibrationprocess. The conventional calibration process to obtain the feedforwardtable is to map the WOT engine output torque as a function of air tofuel ratio AFR at each given engine speed. Then, the feedforward tablecan be obtained by selecting the AFR associated with the maximum WOTtorque output at various engine speeds. For the control system withadaptive learning capability, e.g., step 960, the feedforward table willbe updated, using the calculated Δλ_(DESIRED)(k+1), to compensate forengine-to-engine variations, engine aging, etc.

[0160] In step 960, the feedforward control FFD is updated. This stepupdates the feedforward control portion of the WOT air to fuel ratioAFR. The step calculates the difference between current feedforwardoutput and the final desired air to fuel ratio Δλ_(DESIRED)(k+1), anduses the difference to update the feedforward table gradually. An enginespeed signal 135 is received from an engine speed sensor 136 located inthe engine 161. The engine speed is used to as the input of thefeedforward lookup table. This step runs every perturbation period.

[0161] In step 970, the commanded fuel signal is calculated. This stepcalculates the commanded fuel signal based upon the desired air to fuelratio λ_(DESIRED)(k+1), where the λ_(DESIRED)(k+1) equals toΔλ_(DESIRED)(k+1)+λ_(FFD), and the current engine airflow rate {dot over(m)}_(AIR) 137 received from an air-mass flow sensor 138 located in theengine 161. The desired fuel flow rate {dot over (m)}_(FUEL)(k+1) equalsto current engine airflow rate {dot over (m)}_(AIR) divided by desiredair to fuel ratio λ_(DESIRED)(k+1). This step updates the engine fuelcommanded every engine combustion event or is executed at the same ratethat the fueling step runs at.

[0162] It is a goal of the present control method to maintain theoptimal air to fuel ratio AFR gradient P_(AFR) at zero. With the help ofthe convex property of C_(AFR) as a function of WOT air to fuel ratioAFR, this gradient approach method shall converge with a propercalibrated α.

[0163] In a preferred embodiment, the steps (or instructions) in FIGS.20 and 21 are stored in software or firmware 107 located in memory 111(see FIG. 22) 900. The steps are executed by a controller 121. Thememory 111 can be located on the controller or separate from thecontroller 121. The memory 111 can be RAM, ROM or one of many otherforms of memory means. The controller 121 can be a processor, amicroprocessor or one of many other forms of digital or analogprocessing means. In a preferred embodiment, the controller is enginecontrol unit ECU 121.

[0164] The ECU 121 receives an ionization signal 100 from an ionizationdetection circuit 10. The ECU 121 executes the instructions 107 storedin memory 111 to determine a desired air to fuel ratio AFR. It thenoutputs the desired fuel command 975 to some form of fuel controlmechanism such as a fuel injector 151 located on the engine 161.

[0165] Section E: Closed Loop Cold Start Retard Spark Control UsingIonization Feedback

[0166] Air pollution from automobile exhaust is caused in part byhydrocarbon (HC) emission. A catalyst converter is used in an internalcombustion engine to reduce these pollutants by converting the harmfulmaterials to harmless materials. Because the catalyst converter does notoperate when the temperature of the catalyst is below its operationalpoint, around 70% of the hydrocarbon (HC) emission during the FTP(Federal Test Procedure) cycle is produced during the cold start whenthe catalyst temperature is below its operational point. Variousapproaches have been developed to heat up the catalyst (or achievecatalyst light-off) quickly during the cold start. One way involvesretarding (or delaying) the spark time (or ignition timing) to raise theexhaust temperature. As a result, the catalyst heats up quickly duringthe cold start, reducing HC emission. Since spark retard is limited bypartial burn and misfire, open loop calibration of a retard spark for acold start is performed slowly and conservatively. The conservativenessof the open loop calibration is mainly due to engine-to-enginevariations, engine aging, operational condition variations, etc.

[0167] The retard spark control method of the present invention uses aclosed loop spark timing controller to adjust the engine retard limitduring a cold start. The goal is to run an engine at its retard limitwithout partial burn and misfire during a cold start to reduce the timeneeded to quickly heat up the catalyst. Therefore, use of a retard sparkfor fast heating of a catalyst during a cold start is maximized andcold-start hydrocarbon (HC) emission during a cold start is reduced.

[0168] The feature of the present invention described in Section Ecomprises a subsystem of the ignition diagnostics and feedback controlsystem disclosed in FIG. 13 which uses ionization feedback current toraise the catalyst temperature quickly. The relationship of thesubsystem to the diagnostics and control system is shown in FIG. 13,where the cold start retard spark control is marked as logic block 1000.The method comprises using a closed loop to control the spark retardtiming during an engine cold start to retard the engine spark timing asmuch as possible without engine misfire and with minimum partial burn.The increased exhaust temperature heats up the catalyst quickly which,as a result, reduces HC emissions.

[0169] The closed loop cold start retard spark control system usingionization feedback loop 1010 of the present invention 1000 isillustrated in FIG. 23. A cold start enable flag 1020 (or command orsignal) is used to enable (or activate) the closed loop control. Theenable flag 1020 is generated when the catalyst temperature (measured orestimated) crosses a threshold (1015). The typical range of thethreshold is about 400 degree Celsius.

[0170] Inputs to the closed loop 1010 can include some or all of thesignals discussed below which include a partial burn index 1030, amisfire index 1040, engine speed (RPM) 135, engine load 1060, and enginecoolant temperature 1070. In addition, the loop inputs are not limitedto these signals, but can, in other embodiments, receive additionalinputs. The partial burn index signal 1030 is obtained during aparameter estimation process for misfire detection. The misfire indexsignal 1040 is obtained during a misfire detection calculation byintegrating the ion current during the combustion process and/or thepeak value of the ionization current during the combustion. A thresholdis used for the misfire calculation. The current engine speed 135measured in RPM (Revolutions Per Minute). The engine load 1060 iscalculated as a percentage of maximum load, fueling or the IndicatedMean Effective Pressure (IMEP). The engine coolant temperature signal1070 is a conditioned engine coolant temperature signal.

[0171] The signal output from the closed loop is the cold start sparksignal 1080 which is an ignition timing signal which will fire a sparkplug at a Crank-angle After Top Dead Center (CATDC). Normally, the sparkplug in a cylinder will be fired at its MBT timing normally locatedbefore the top dead center (TDC). However, the ignition timing can beretarded (or delayed) causing the spark plug to fire at retard timing(e.g., after top dead center) to increase the exhaust gas temperature,thereby heating the catalyst quickly.

[0172] The closed loop retard spark control using ionization currentfeedback 1010 consists of four major components or functions (see FIG.23) which include an error and gain generator 1100, a proportional andintegration (PI) control processing block 1200, a default spark timingprocessor 1210, and an adaptive learning apparatus 1220. They are listedbelow with detailed descriptions.

[0173]FIG. 23 illustrates four major components of the closed loopcontroller 1010 of the present invention. The first is the error andgain generator 1100. The partial burn index signal 1030 and the misfireindex signal 1040 are input to the error and gain generator 1100. In apreferred embodiment, the error and gain generator 1100 can be aprocessor, microprocessor or any form of processing means. The misfireindex is calculated in Section A of this application by using theionization current signal, and the partial burn index can be calculatedusing the information calculated during the misfire detection process,such as area integration of the ionization current over the combustionwindow and the peak value over the combustion window. By setting properthresholds higher than the misfire ones, partial burn index can beobtained by comparing the thresholds and calculated value. The error andgain generation generator 1100 outputs two signals, CL_error 1090 andCL_gain 1095, where CL_gain consists of both proportional andintegration gains. Signals CL_error 1090 and CL_gain 1095 can be any ofthree output values depending on the states of the partial burn indexand the misfire index, “negative one”, “one” and a “calibratablepositive value”:

[0174] The partial burn index signal 1030 and the misfire index signal1040 are input to the error and gain generator 1100 (see FIG. 24). Checkthe signals' states 1115. If both the partial burn index 1030 and themisfire index 1040 are inactive 1120, then a closed loop error signalCL_error 1090 is set to “one”, the proportional gain of a closed loopgain signal CL_gain 1095 is set to “zero,” while the integration gain ofCL_gain is set to a calibratable positive value 1130. The typical rangeof the calibration positive value is between 0.01 and 2. In response tothese inputs, the control output 1205 of the proportional andintegration (PI) control processing block 1200 will move the closed loopcontrol's output signal 1080 in the retard direction 1140, therebydelaying the ignition timing. Thus, the firing of the spark plug isdelayed for that cylinder, causing the spark plug to fire at a moreretard crank-angle than the previous ignition event. FIG. 25a shows howthe control method works for this case.

[0175] If the partial burn index is active and the misfire index isinactive 1150, then CL_error 1090 is set to negative “one,” theproportional gain of CL_gain 1095 is set to “zero,” while theintegration gain of CL_gain 1095 is set to a calibratable positive value1160 at a similar range to case 1. In response to these inputs, thecontrol output 1205 of the proportional and integration (PI) controlprocessing block 1200 will move the spark timing output signal 1080 inthe spark advance direction 1170. Thus, the firing of the spark plug isadvanced for that cylinder causing the spark plug to fire before theprevious spark timing. FIG. 25b shows how the control method works forthis case.

[0176] If the misfire index signal 1040 is active 1180, then CL_error1090 is set to negative “one,” the proportional gain of CL_gain 1095 isset to “zero,” while the integration gain of CL_gain 1095 is set to acalibratable positive value greater than cases 1 and 2. The upper boundof the calibratable positive value can reach 4 to avoid misfire in nextcombustion event. In response to these inputs, the proportional andintegration (PI) control processing block will add a calibratablenegative value (or offset, e.g., −5 degree) to the PI integrator causingits control output 1205 to move the spark timing output signal (orignition timing signal) 1080 in the spark advance direction to avoidmisfire and return to either case 1 or case 2 (1195). When a misfireoccurs, the PI integrator is reset by adding a calibratable sparkadvance (a negative value) to the existing integrator register toeliminate the misfire quickly. FIG. 25c shows how the control methodworks for this case.

[0177] Therefore, the general method of the present invention comprisesrunning the engine spark time at its retard limit. That is, to run theengine at a maximum allowable retard time without misfire and withminimum partial burn of the air-fuel (A/F) mixture. Thus: 1) when theengine is not at partial burn, the spark timing moves in the retarddirection at a certain rate 1140, such as quarter crank degree percombustion event; 2) when the spark timing is at partial burn, the sparktiming moves in the advance direction at a certain rate 1170 similar tocase 1; and 3) when a misfire occurs, a correction will be added to thePI integrator to move the spark timing in the advanced direction quicklyto avoid further misfire 1195.

[0178] The second major component is the proportional and integration(PI) control processing block 1200. In a preferred embodiment, only theintegration portion of the PI controller 1200 or integration controller1200 is used for closed loop control of the retard spark during a coldstart. Both the integration gain CL_gain 1095 and the integration errorCL_error signals 1090 are provided by the error and gain generator 1100to the PI controller 1200.

[0179] The third major component is the default spark timing processor1210. Default (or reference) spark timing is stored in a lookup table1213 which is a function of engine speed 135, engine load 1060, enginecoolant temperature 1070 and other factors. It can be obtained from theengine calibration process. The lookup table 1213 can be stored inmemory located in the default spark timing processor 1210 or in adiscrete memory chip. Due to the adaptive learning feature of thisprocessor or controller 1210, the default spark timing table 1213 ismodified by input 1225 (the adaptive learning output signal) from theadaptive learning apparatus 1220 so that the default (or reference)spark timing signal 1215 is compensated by the default spark timingprocessor 1210 or timing processor 1210 to account for engine-to-enginevariation, engine aging, and other related factors. The output from thedefault timing apparatus 1210 is the reference signal 1215 which issummed with the output 1205 of the PI controller 1200 by summer 1230 toproduce the cold start spark signal 1080.

[0180] The fourth major component is the adaptive learning apparatus1220. The adaptive learning apparatus 1220 compares (in comparator 1224)the current cold start spark timing output signal ST_(CURRENT) 1080 (orcurrent spark timing signal 1080 or current ignition timing correctionsignal 1080) with a default cold start spark timing signal ST_(DEFAULT)1221 generated from a lookup table 1223 based upon the engine's currentoperating conditions (135, 1060, 1070) which serve as inputs to theadaptive learning block 1220. The lookup table 1223 can be stored inmemory located in a processor 1222 or in a discrete memory chip. Whenthe engine operational condition is close to a neighborhood of any meshpoint of default spark timing lookup table 1223, the spark timing valueST_(TABLE)(OLD) of the lookup table 1223 at that specific pointST_(TABLE) will be replaced by ST_(TABLE)(NEW) using the followingformula:

ST _(TABLE)(NEW)=ST _(TABLE)(OLD)+β*(ST _(CURRENT) −ST _(DEFAULT))1226,

[0181] where β is a calibratable positive coefficient with a typicalvalue of 0.02. In order to limit the capability of the adaptivealgorithm for safety and other reasons, the maximum allowed change ofST_(TABLE)(NEW) 1226 from the default calibration can not be greaterthan a calibratable crank degree. If the change of calculatedST_(TABLE)(NEW) 1226 exceeds the limit, the boundary value will be usedas ST_(TABLE)(NEW) 1226.

[0182] In one preferred embodiment, the adaptive learning apparatus 1220comprises a processor 1222, a comparator 1224, and software stored inmemory comprising instructions 1227 (which can be the same memory 1223that table 1223 is stored in or in different memory). For the defaultspark timing lookup table, see FIG. 26. The operating conditions includeengine speed (rpm) 135, engine load 1060 and coolant temperature 1070.The adaptive learning apparatus 1220 together with the default sparktiming processor 1210 constitute the feedback portion 1217 or feedbackcontroller 1217 of the closed loop 1010.

[0183] Section F: Robust Multi-Criteria MBT Timing Estimation UsingIonization Signal

[0184] It is a goal of an ignition system of an internal combustionengine to time the ignition/spark so that the engine produces itsmaximum brake torque with a given air to fuel mixture. Thisignition/spark timing is referred to as the minimum timing for besttorque or MBT timing. The mean brake torque of an internal combustionengine is a function of many factors such as air to fuel ratio,ignition/spark timing, intake air temperature, engine coolanttemperature, etc. By fixing all the factors that affect the mean braketorque of an internal combustion engine, the engine mean brake torque isa convex function of ignition/spark timing when the ignition/sparktiming varies within a certain range, where MBT timing corresponds tothe peak location of the convex function. If the spark timing isretarded or advanced relative to the MBT timing, the mean brake outputtorque is not maximized. Hence, running an internal combustion engine atits MBT timing provides the best fuel economy. Therefore, it isdesirable to find criteria which can be used to produce a reliableestimate of MBT timing for closed loop control of engine ignition/sparktiming. This invention proposes a method to determine engine MBT timingat current operational conditions using a spark plug ionization signal.

[0185] Different from the cylinder pressure signal that exhibits arelatively stable pressure curve throughout engine operating conditions,the waveform shape of a spark plug ionization signal can change withvarying loads, speeds, spark timings, air to fuel A/F ratios, exhaustgas re-circulation EGR rates, etc. Searching for the ionization postflame peak that is supposed to be lined up with the peak pressurelocation is not always a reliable MBT timing criteria due to thedisappearance of this peak at low loads, retarded spark timing, lean A/Fratios, or higher EGR rates. The present invention solves this problemby establishing a robust multi-criteria MBT timing estimation methodutilizing different ionization signal waveforms that are generated underdifferent engine operating conditions.

[0186] The spark plug ionization signal 100 is a measure of the localcombustion mixture conductivity between the spark plug electrodes duringthe combustion process. This signal 100 is influenced not only by thecomplex chemical reactions that occur during combustion, but also by thelocal temperature and turbulence flow at the spark gap during theprocess. The ionization signal 100 is typically less stable than thecylinder pressure signal that is a measure of the global pressurechanges in the cylinder.

[0187] So far, the MBT timing control strategies appearing in the priorart are predominantly based on post flame peak detection. The post flamepeak detection usually lines up with the peak pressure location. It hasbeen recognized that the MBT timing occurs when the peak pressurelocation is around 15° After Top Dead Center (ATDC). By advancing ordelaying the spark timing until the second peak of the ionization signalpeaks around 15° ATDC, it is assumed that the MBT timing is found.

[0188] Unfortunately, the second peak of the ionization signal 100 doesnot always appear in the ionization signal 100 waveform at all engineoperating conditions. At light loads, lean mixtures, or high EGR rates,the second peak can be difficult to identify. Under these circumstances,it is almost impossible to find the MBT timing using the 2^(nd) peaklocation of the ionization signal 100.

[0189] The present invention establishes multiple MBT timing criteria toincrease the reliability and robustness of MBT timing estimation basedupon spark plug ionization signal 100 waveforms. Therefore, the presentmethod optimizes ignition timing by inferring from the ionization signalwhere the combustion event is placed in the cycle that corresponds tothe MBT timing.

[0190]FIG. 11 shows a typical ionization signal 100 versus crank angle.Different from a pressure signal waveform, an ionization signal 100waveform actually illustrates more details of the combustion process.For example, the ionization signal 100 waveform shows when a flamekernel is formed and propagates away from the gap, when the combustionis accelerated intensively, when the combustion reaches its peak burningspeed, and when the combustion ends. An ionization signal 100 usuallyconsists of two peaks. The first peak 162 of the ionization signal 100represents the flame kernel growth and development, and the second peak166 is caused by re-ionization due to the temperature increase resultingfrom pressure increase in the cylinder.

[0191] The combustion process of an internal combustion engine 161 isusually described using the mass fraction burn versus crank angle.Through mass fraction burn, we can find when the combustion has its peakburning acceleration and peak burning velocity. Locating these events ata specific crank angle will allow us to obtain the most efficientcombustion process. In other words, we can find MBT timing through theseevents. The inflexion point 163 right after the first peak 162 can becorrelated to the maximum acceleration point of the cylinder pressuresignal. This point is usually between 10% to 15% mass fraction burned(see FIG. 27, point 163 of case 1). The inflexion point 165 right beforethe second peak 166 of the ionization signal 100 correlates well withthe maximum heat release point of the cylinder pressure signal and islocated around 50% mass fraction burned (see FIG. 27, point 165 of case1). In addition, the second peak 166 is related to or correlates to thepeak pressure location of the pressure signal (see FIG. 27, point 166 ofcase 1).

[0192] At MBT timing, the maximum flame acceleration point is located atTop Dead Center TDC. It has been established that the 50% mass fractionburn is located around 8-10° After Top Dead Center (ATDC) and the peakpressure location is around 15° ATDC when a combustion process starts atMBT timing. Combining all three individual MBT timing criterion orcriteria into one produces increased reliability and robustness of theMBT timing prediction.

[0193]FIG. 27, cases 1, 2 and 3, illustrate three waveforms that theionization signal takes at various engine operating conditions (case1—1500 rpm, 2.62 bar BMEP, EGR=0%; case 2—1500 rpm, 2.62 bar BMEP,EGR=15%; case 3—3000 rpm, WOT, cylinder #3): Case 1 illustrates a normalwaveform where both peaks 162, 166 are present in the waveform. In Case2, the second peak 166 does not show up due to the relatively lowtemperature resulting from the high EGR, a lean mixture or a low loadcondition, or from a combination of these factors. In Case 3, the firstpeak 162 merges with the ignition signal due to the longer crank angleignition duration resulting from a relatively constant spark duration athigh engine speed.

[0194] Locations 162-166 in FIG. 28 are defined as follows: 162, thefirst peak location of the ionization signal; 163, the maximum flameacceleration location (close to or correlated to Top Dead Center (TDC)at MBT timing); 164, the valley location of the ionization signal; 165,the maximum heat release location (correlated to 50% burn location andclose to 8-10% After Top Dead Center (ATDC) at MBT timing); and 166, thesecond peak location (correlated to peak cylinder pressure location andclose to 15-17° After Top Dead Center (ATDC) at MBT timing).

[0195] In a preferred embodiment, the present invention uses MBT timingestimation criterion which is a combination of the maximum flameacceleration location 163, the 50% burn location 165, and the secondpeak location 166 which are shown in cases 1 through 3 of FIG. 27.

[0196] When the ionization signal 100 waveform takes on the waveform ofcase 1, all three MBT timing criteria will be used due to theiravailability. That is,

L _(MBT)=(L ₁₆₃+(L ₁₆₅ −L _(50%BURN))+(L ₁₆₆ −L _(PCP)))/3,  (Equation1)

[0197] where L_(MBT) is the estimated MBT timing location, L₁₆₃ is themaximum flame acceleration location, L₁₆₅ is the maximum heat releaselocation, L_(50%BURN) is the 50% burn location of the pressure signalwhen the engine is running at MBT timing, L₁₆₆ is the second peaklocation, and L_(PCP) is the Peak Cylinder Pressure location when theengine is running at MBT timing. L_(50%BURN) and L_(PCP) are typicallylocated around 8-10° and 15-17° ATDC respectively. Since MBT timing forL_(50%BURN) and L_(PCP) varies as a function of engine operationalconditions, in a preferred embodiment a lookup table containing valuesof L_(50%BURN) and L_(PCP) can be used when calculating the desired MBTlocation for different operating conditions.

[0198] For case 2, the only available MBT criterion is location 163.Therefore, equation 1 reduces to:

L _(MBT) =L ₁₆₃,  (Equation 2)

[0199] where L_(MBT) is the estimated MBT timing location.

[0200] For case 3, locations L₁₆₅ and L₁₆₆ are available. The MBT timingcalculation utilizes both L₁₆₅ and L₁₆₆ calculate the estimated timinglocation as follows:

L _(MBT)=((L ₁₆₅ −L _(50%BURN))+(L ₁₆₆ −L _(PCP)))/2,  (Equation 3)

[0201] As with Case 1, both L_(50%BURN) and L_(PCP) can be selected tobe constant values (i.e., (8-10°) and (15-17°), respectively) or one canuse the outputs of lookup tables to reflect variations due to engineoperational conditions. The lookup tables 113 can be stored in memory111. Any form of memory such as RAM, ROM or even an analog memorystorage such as magnetic tape can be used. The data in the lookup tablecan be accessed by a processor, microprocessor, controller, enginecontrol unit, or any of a number of processing or controlling means 122.

[0202]FIG. 28 is a block diagram of the robust multi-criteria MBT timingestimation method of the present invention. FIG. 29 illustrates a logicblock diagram of the present invention 1800. The engine control unit ECU121 receives the ionization signal 100 from an ionization detection unit10 (Step 1801). (See FIG. 30). Next, the processor 122 in the ECUexecutes software or firmware 107 stored in memory (which can be thesame memory 111 that the lookup table 113 is stored in or differentmemory). The software 107 comprises instructions to determine which casethe ionization signal 100 waveform fits, i.e. case 1, 2 or 3 (1810). Ifionization signal 100 fits case 1 (1815), calculate locations L₁₆₃, L₁₆₅and L₁₆₆ (1817). Next, the software 105 calculates MBT timing byexecuting equation 1,

L _(MBT)=(L ₁₆₃+(L ₁₆₅ −L _(50%BURN))+(L₁₆₆ −L _(PCP)))/3(1820).

[0203] If ionization signal 100 fits case 2 (1825), calculate locationL₁₆₃ (1827). Next, the software 105 calculates MBT timing by executingequation 2, L_(MBT)=L₁₆₃ (1830). If ionization signal 100 fits case 3(1835), calculate locations L₁₆₅ and L₁₆₆ (1837). Next, the software 105calculates MBT timing by executing equation 3,

L _(MBT)=((L ₁₆₅ −L _(50%BURN))+(L ₁₆₆ −L _(PCP)))/2(1840).

[0204] The ECU 121 calculates an ignition timing control signal V_(in),using a closed loop MBT timing controller (e.g., the one described inSection G), and outputs it to a driver circuit 75 (1850). The drivercircuit 75 charges the ignition coil 12 which current to flow betweenthe spark plug 14 electrodes. The air to fuel (A/F) mixture between theelectrodes conducts heavily, dumping the energy stored in the ignitioncoil 12 in the spark plug 14 gap. The sudden release of energy stored inthe coil 12 ignites the air to fuel (A/F) mixture in the cylinder.

[0205] Section G: Closed Loop MBT Timing Control Using IonizationFeedback

[0206] This feature of the invention comprises a method and apparatus tocontrol the engine (minimum timing for the best torque (MBT) sparktiming in a closed loop using either ionization or pressure feedback.Both an ionization signal and an in-cylinder pressure signal can be usedfor calculating and estimating engine MBT timing criterion (or criteria)for each individual cylinder, where this criterion provides a relativemeasure of how far away the current engine spark timing is from MBTtiming. See Sections F, “Robust Multi-Criteria MBT Timing EstimationUsing Ionization Signal,” and J, “The Determination of MBT TimingThrough the Net Pressure Acceleration of the Combustion Process”. Whenthe engine is neither knock spark limited (i.e., the MBT spark is moreadvanced than knock limited spark timing), nor misfire/partial-burnlimited (i.e., the desired spark is more retarded (or delayed) than themisfire/partial-burn limited spark timing), the engine is operated in aclosed loop MBT timing control mode using MBT timing criterion feedback.

[0207] On the other hand, when the engine is knock limited, a knocklimit manager maintains operation of the engine at its non-audible knocklimit using a closed loop knock limit control. When the engine ismisfire/partial-burn limited (e.g., during the cold start, it isdesirable to run the engine at its retard limit to heat up the catalystquickly, see Section E), the misfire limit manager maintains the engineat its misfire/partial-burn limit.

[0208] It is desirable to run an automobile internal combustion engineat its MBT spark timing, if possible, for improved fuel economy. Due tothe lack of a combustion feedback control system in the prior art, theignition timing is controlled in open loop based upon an MBT timingtable based upon the engine mapping data. One disadvantage of thisapproach is that it requires a long calibration process and the MBTtiming control system is sensitive to changes in system parameters. Inother words, the open loop MBT timing control is not able to compensatethe MBT spark timing changes due to engine-to-engine variations, engineaging, and engine operational condition variations (altitude,temperature, etc.). In addition, the long calibration process extendsthe development duration and increases costs. An open loop ignitiontiming control limits its calibration to a conservative calibration sothat the engine cannot be operated at its physical limits (e.g., knocklimit). This, in turn, reduces fuel economy.

[0209] The present invention uses a closed loop MBT timing control, withthe help of knock and misfire/partial burn limit management, to improvethe robustness of an open loop ignition timing control. This, in turn,reduces engine system calibrations, and improves engine fuel economy.

[0210] The present invention comprises a subsystem of an ignitiondiagnostics and feedback control system using ionization feedback. Therelationship of this subsystem to the diagnostics and control system isshown in FIG. 13 and the logic blocks are labeled 1450, (1430, 1490,1495), and 1460. This subsystem comprises a closed loop controller whichuses estimated MBT timing criteria generated from either (or both) anionization signal 100 and an in-cylinder pressure signal and ignitiondiagnostics (knock, partial-burn, and misfire) to control engineignition timing. When the engine is not knock limited, it operates atits MBT timing for the best fuel economy. When the engine is knocklimited, the engine runs at its non-audible knock limit for the besttorque output. When the engine is misfire/partial-burn limited, theengine is maintained at its misfire/partial-burn limit.

[0211] Three different embodiments of the closed loop MBT timing controlarchitecture are discussed below: a) a cylinder-by-cylinder approach, b)an average approach, and c) a mixed approach. They are differentiated bywhether the MBT timing is controlled cylinder-by-cylinder or globally.The first embodiment controls the engine MBT spark timing of eachcylinder individually. The MBT, knock, and misfire information of agiven cylinder is used to control that cylinder's MBT timing. The secondembodiment uses an averaged approach. To be more specific, all cylindersare controlled using a single MBT timing control parameter. The thirdembodiment uses a mixed approach. That is, the engine misfire and knockare controlled individually, while the MBT timing is controlledglobally. The following is a detailed description of each embodiment.

[0212] In the cylinder-by-cylinder approach, the MBT timing criterion1435, the knock information 1400 and the misfire information 1410 ofeach individual cylinder are calculated separately. Furthermore, theengine's individual MBT timing controller 1430 controls the ignitiontiming (see FIG. 31). The cylinder-by-cylinder closed loop controller1430 runs every ignition event. The output of this closed loopcontroller is the recommended MBT timing signal 1480 for individualcylinders. The inputs to this closed loop controller 1430 are listedbelow:

[0213] The individual cylinder MBT criterion 1435 or individual cylinderMBT timing criterion 1435 is calculated from an ionization signal 100 orin-cylinder pressure signal generated using a parameter estimationmethod (see Sections F, “Robust Multi-Criteria MBT Timing EstimationUsing Ionization Signal” and J, “The Determination of MBT Timing Throughthe Net Pressure Acceleration of the Combustion Process”) for theionization case. This parameter discloses whether the current enginespark is before or behind the MBT spark timing for that individualcylinder.

[0214] Individual cylinder knock information 1400 consists of a knockintensity parameter 1402 and a knock flag 1404. The knock intensity 1402indicates how severe the knock is and the knock flag 1404 indicates ifan audible knock exists or not. Note that both the knock intensity 1402and the knock flag 1404 can be obtained from either ionization 100 orin-cylinder pressure signals.

[0215] Individual cylinder misfire information 1410 consists of bothpartial-burn 1412 and misfire flags 1414. Again, both partial-burn 1412and misfire flags 1414 can be obtained from ionization current 100 orin-cylinder pressure signals.

[0216] The cylinder-by-cylinder closed loop MBT timing controller 1430of the present invention consists of three major subsystems: 1) a closedloop MBT timing proportional and integral (PI) controller 1440, 2) aknock spark advance limit manager 1450, and 3) a misfire spark retardlimit manager 1460. The MBT criterion 1435 is compared with the MBTreference signal 1437 (1500), and the resulting error 1438 is input tothe PI controller 1440 (1510) (See FIG. 32). The output 1442 of the PIcontroller 1440 provides the desired MBT timing if the engine 161 isneither knock limited, nor misfire limited. The saturation manager 1470outputs the ignition/spark timing signal 1480 used to control theignition timing for that particular cylinder. In a preferred embodiment,the saturation manager 1470 can prevent output windup.

[0217] The knock limit manager 1450 provides a knock limit signal 1452that provides the maximum spark advance allowed at the current engine161 operational conditions. For example, when the engine 161 is notknock limited, the knock manager 1450 provides a spark advance limitsignal 1452 associated with the engine's 161 physical configuration andcalibration. When the engine 161 is knock limited, the knock manager1450 provides a spark advance limit signal 1452 that makes it possiblefor the engine 161 to run at its knock limit, or in other words, allowsthe engine 161 to run with light or non-audible knock.

[0218] Similarly, the misfire limit manager 1460 provides a misfirelimit signal 1462. For example, when the engine 161 is withoutpartial-burn or misfire, it provides the engine 161 with a physicalretard spark limit signal 1462 associated with the engine's 161 physicalconfiguration and calibration. When the engine 161 spark timing ismisfire limited, it provides a retard limit signal 1462 to allow theengine 161 to operate at its partial-burn/misfire limit. The retardspark limit signal 1462 is input to the saturation manager 1470.

[0219] When the engine 161 is either knock or misfire limited (that is,the saturation manager 1470 is active), the corresponding knock 1452 orretard limit 1462 information is forwarded by the saturation manager1470 and is used to reset the PI integrator (see integration reset logicbelow) to avoid integration rewinding problems.

[0220] The PI controller 1440 of FIG. 31 (see FIG. 33 for a detailedconfiguration) consists of proportional 1441 and integral controller1444, a feedforward controller 1446 with adaptive learning capability1447, and an integration reset logic manager 1448 to prevent integrationcontrol overflow and rewinding problems. The functionality of theselogic devices is described below:

[0221] The feedforward controller 1446 is designed to modify open loopMBT timing over the given engine operation map. In addition, an adaptivelearning manager 1447 is used to compensate for engine-to-enginevariation, engine aging, and operation environmental variation, etc. Thefeedforward controller 1446 outputs feedforward output 1449.

[0222] The proportional 1441 and integral controller 1444 output aproportional control output 1443 and an integral controller output 1445respectively. The proportional control output 1443 is produced bymultiplying the MBT error input 1438 by the proportional gain (1520)producing a proportional error signal 1443. The typical value for theproportional gain is around 0.2. The integral controller output 1445 isproduced by multiplying the integrated MBT error 1438 by the integralgain (1530) producing an integrated error signal 1445. The typical valuefor the integral gain is around 0.1. The integrated error signal can bereset when the engine is knock or misfire limited (see below). Theproportional error signal 1443, the integrated error signal 1445, andthe feedforward output 1449 are summed to produce timing signal 1442.

[0223] The integration reset manager 1448 is a logic device 1448 becomesactive when the engine 161 is knock limited or misfire limited. Thereset integrated error signal is calculated in such a way that the sum1442 of the feedforward 1449, proportional 1443, and integral controller1445 outputs are limited by either the knock 1450 or the misfire limit1460 managers. That is, if the engine is knock or misfire limited, thenthe integral error signal is reset (1540) such that the final outputstays right at either the knock limit or misfire/partial-burn limit.

[0224] The second major subsystem, the knock spark advance limit manager1450 controls the closed loop knock limit. It includes a PI controller51441, 51444, 51446, 51448, 51447, a knock error and gain generator 1454and a saturation manager 1470.

[0225] Only the integration portion of the PI controller (whichcomprises blocks 51441, 51444, 51446, 51448, 51447 in the knock manager1450) is used for closed loop knock limit control 1450 (see FIG. 34)since the proportional gain is set to zero at all times. The integrationgain and the error used by the PI controller 51441, 51444, 51446, 51448,51447 are provided by the knock error and gain generator 1454 (1552)(see FIG. 35). The integral reset logic device 51448 is used to resetthe integral gain and integrator controller 51444 output 51445 to avoidoverflow and rewinding when the output is saturated (1540).

[0226] The closed loop knock spark advance limit manager 1450 (see FIG.34 for a detailed configuration) consists of a knock error and gaingenerator 1454 which is operably connected to the PI controller 51441,51444, 51446, 51448, 51447 disclosed in the knock manager 1450 in FIG.34.

[0227] The knock error and gain generator 1454 is a logic block ordevice in which both the knock intensity 1402 and the knock flag 1404,calculated in a preferred embodiment by using the ionization currentsignal 100, are used as inputs. The generator 1454 outputs two signals,“Error” 1455 and “Gain” 1459, where “Gain” 1459 consists of bothproportional and integration gains. Both the “Error” 1455 and “Gain”1459 outputs are generated using the knock intensity 1402 and knock flag1404 signals and are divided into three states: a) no knock, b)inaudible knock, and c) audible knock.

[0228] The no knock state occurs when the knock flag signal 1404 isinactive and the knock intensity 1402 is below the no knock threshold.In this case, if the knock flag signal 1404 is inactive and the knockintensity 1402 is below the no knock threshold (1554), the “Error”output 1455 is set to one. In addition, the proportional gain of the“Gain” output 1459 is set to zero, while the integration gain is set toa calibratable positive value (1556) such as 0.2. Thus, the proportionalcontrol output 51443 of the PI controller 51441, 51444, 51446, 51448,51447 is zero, while the integral controller output 51445 equals apositive value. The knock error and gain generator 1454 moves the closedloop timing output 51442 in the advance direction between the hardadvance lower limit 1456 and the hard advance upper limit 1458 since theintegration reset logic 51448 resets the integrator to limit the timingoutput within the timing boundary defined by 1456 and 1458 if the timingoutput 51442 is outside the boundary.

[0229] The inaudible knock state occurs when the knock flag signal 1404is inactive and the knock intensity 1402 is beyond the knock threshold.This is the desired operational condition when the engine 161 is knocklimited. In this case, if the knock flag signal 1404 is inactive and theknock intensity 1402 is beyond the non-audible knock threshold (1560),the “Error” output 1455 is set to zero. In addition, the proportionalgain of the “Gain” output 1459 is set to zero, while the integrationgain remains at the calibrated value (1562) as in the no knock case.Thus, the proportional control output 51443 of the PI controller 51441,51444, 51446, 51448, 51447 is zero, while the integral controller output51445 remains at its previous positive value. This allows the timingadvance limit signal 1452 to remain unchanged.

[0230] The audible knock state occurs when the knock flag 1404 becomesactive. In this case, if the knock flag 1404 is active (1565), the“Error” output 1455 is set to negative one. In addition, theproportional gain of the “Gain” output 1459 is set to zero, while theintegration gain is set to a calibratable value (1567) such as 0.4.Plus, a calibratable negative value is added to the integrator to movethe spark timing in the retard direction to avoid engine knock and toreturn to either case b or case a, immediately.

[0231] The general method of the closed loop knock limit management isto allow the engine to run its spark timing right at its advance limit(hard advance upper limit 1458) or as close as possible. That is, whenthe engine 161 is knock limited, the engine 161 will run at its maximumadvance timing limit with a inaudible knock (i.e., case b, timing atknock limit DBTDC). When the engine 161 is not knock limited, sparktiming signal 1452 moves in an advanced direction at a certain rateuntil it reaches the hard limit. When the engine 161 runs right at itsinaudible knock limit, the spark timing limit signal 1452 remainsunchanged. And when the engine 161 runs with an audible knock, acorrection will be added to the knock PI integrator 51441, 51444, 51446,51448, 51447 to move the spark timing signal 1480 in the retarddirection quickly to avoid further engine knocking.

[0232] The feedforward knock spark limit controller 51446 and theadaptive knock spark limit controller 51447 set a feedforward sparklimit that is a function of engine speed 135 and engine load 1060. Itcan be obtained through the engine calibration process. Due to theadaptive learning feature of this controller 51447, the feedforwardspark limit is modified based upon the output of the adaptive learningmethod so that the feedforward spark limit is able to compensate forengine-to-engine variation, engine aging and so on. The adaptivelearning controller 51447 compares the current spark limit with thefeedforward timing limit signal 51442 at the current engine operatingconditions (such as engine speed and load) to correct the feedforwardtiming limit 51442 adaptively.

[0233] The third major subsystem, the closed loop misfire controller1460 or misfire retard limit manager 1460 controls closed loop misfire.The closed loop misfire controller 1460 (see FIG. 36 for a detailedconfiguration) consists of a misfire error and gain generator 1463.Here, the PI controller 61441, 61444, 61446, 61448, 61447 is used togenerate a spark advance limit signal. The integration gain and theerror used by the PI controller 61441, 61444, 61446, 61448, 61447 areprovided by the misfire error and gain generator 1463 (1572) (see FIG.37).

[0234] Only the integration portion of the PI controller 61441, 61444,61446, 61448, 61447 is used for closed loop control of the retard sparklimit. Both the integration gain and error are provided by the error andgain generation block (or error and gain generator) 1463. When a misfireoccurs, the PI integrator 61444 is reset by adding a calibratable sparkadvance (a positive value) to the existing integrator register toquickly eliminate the misfire.

[0235] In the misfire error and gain generator block 1463, both thepartial-burn flag 1412 and the misfire flag 1414, which in a preferredembodiment, is calculated using the ionization current signal 100, areused as inputs. This block outputs signals, “Error,” 61455 and “Gain,”61459, where the “Gain” signal consists of both the proportional and theintegration gains. They can be divided into three states: d) bothpartial burn 1412 and misfire 1414 flags are inactive, e) partial burnflag 1412 is active, but the misfire flag 1414 is not active, and f)active misfire flag (or index) 1414.

[0236] In the case where both partial burn 1412 and misfire 1414 flagsare inactive (1574), the “Error” output 61455 is set to a negative one,the proportional gain of the “Gain” output 61459 is set to zero, whilethe integration gain of the “Gain” output 61459 is set to a calibratablepositive value (1576) such as 0.2. Thus, the proportional control output61443 of the PI controller 61441, 61444, 61446, 61448, 61447 is zero,while the integral controller output 61445 reduces. This allows theclosed loop control output 1462 to move in the retard direction until itreaches the hard retard upper limit 1468. Note that when ever output1462 is not between the hard upper and lower limits (1468 and 1466), theintegrator will be reset by the reset logic 61448 such that the outputstays within the range.

[0237] In the case where the partial burn flag 1412 is active, but themisfire flag 1414 is not active (1578), the “Error” 61455 output is setto one, and the proportional gain of the “Gain” output 61459 is set tozero, while the integration gain of the “Gain” output 61459 is set to acalibratable positive number (1580) same as case d. Thus, theproportional control output 61443 of the PI controller 61441, 61444,61446, 61448, 61447 is zero, while the integral controller output 61445is set to a positive value. This allows the spark timing 1462 to move atan advance direction.

[0238] In the case where the misfire flag (or index) 1414 is active(1582), the “Error” output 61455 is set to one, and the proportionalgain of the “Gain” output 61459 is set to zero, while the integrationgain of the “Gain” output 61459 is set to a calibratable value greaterthan case e (1584) such as 0.4. Thus, the proportional control output61443 of the PI controller 61441, 61444, 61446, 61448, 61447 is zero,while the integral controller output 61445 moves in an advancedirection. A calibratable positive value is added to the PI integrator61444 to immediately move the closed loop control output signal 1462 inthe advanced direction to avoid misfire and to return to either case eor case d, immediately.

[0239] The general method of the closed loop misfire spark limit controlis to provide the engine spark timing signal 1462 right at its retardlimit. That is, to allow the engine to run at its maximum allowed retardtime (i.e., maximum delay from the MBT timing for that cylinder) withouta misfire and with minimum partial burn. When the engine 161 is not atthe partial burn state, the spark timing signal 1462 will move in theretard direction at a certain rate determined by the integration gaincalibrated in case d. When the engine 161 is at partial burn, the sparktiming 1462 moves in the advance direction at a certain rate calibratedby the integration gain defined in case b. In the case where a misfireoccurs, a correction will be added to the PI integrator 61444 to movethe spark timing signal 1462 in the advance direction quickly to avoidfurther misfires.

[0240] The feedforward retard spark limit controller 61446 and theadaptive retard spark limit learning controller 61447 set a feedforwardretard spark limit that is a function of engine speed 135 and engineload 1060. It can be calculated during the engine's calibration process.Due to the adaptive learning feature of the controller 61447, thefeedforward spark limit is modified based upon the output of theadaptive learning method so that the feedforward spark limit is able tocompensate for engine-to-engine variations, engine aging, etc. Theadaptive learning circuit 61447 compares the current retard spark limitwith the default limit at the current engine operating conditions (suchas engine speed 135 and load 1060) to correct the feedforward retardspark limit adaptively.

[0241] As stated supra, the second embodiment of the MBT timing controlarchitecture uses an average approach. In this embodiment, the knockinformation 1400 and the misfire information 1410 of all the individualcylinders are used to calculate the worst case knock 1406 and worst casemisfire information 1416 which is then fed into the advance 1450 and theretard limit 1460 managers. A knock processor 1408 and a misfireprocessor 1418 perform the calculations. In addition, the latest engineMBT criterion 1435 is used to control the ignition timing, see FIG. 38.

[0242] The worst case knock information 1406 consists of both a worstcase knock flag 1407 and a worst case knock intensity 1409. The worstcase knock flag 1407 is set to active as long as one of the individualcylinder knock flags 1404 is active over one engine cycle. The worstcase knock intensity 1409 is equal to the maximum of all knockintensities 1402 for all the cylinders over one engine cycle.

[0243] Similar to the worst case knock information 1406, the worst casemisfire information 1416 consists of both a worst case partial-burn flag1417 and a worst case misfire flag 1419. As long as one of thepartial-burn 1412 or misfire 1414 flags is active over one engine cycle,the corresponding worst case partial-burn 1417 or misfire flag 1419 isset to active over one engine cycle.

[0244] The function of the MBT timing controller 1490 of the averageapproach embodiment is similar to the function of the controller used inthe cylinder-by-cylinder method embodiment (compare FIG. 31 and FIG.38). In addition, the average approach method uses only one PIcontroller 1440, one knock limit manager 1450 and one misfire limitmanager 1460 to generate one mean MBT ignition timing control signal1480 which is used to control the ignition for all cylinders. Adifference between this embodiment and the cylinder-by-cylinderembodiment is that the worst case knock 406 and misfire 1416 informationis used by the knock advance limit 1450 and the misfire retard limit1460 managers respectively (see FIG. 38). In addition, current MBTcriterion (or criteria) 1435 for the current cylinder is input to theMBT PI controller 1440. The advantage of the average method is that onlyone PI controller 1440 is used for all cylinders which reduces thethroughput requirement. However, since this method does not useindividual cylinder knock and misfire limit management, a moreconservative knock and misfire control of each cylinder occurs since onemean signal 1480 is used for all cylinders.

[0245] As stated supra, the third embodiment of the MBT timing controlarchitecture uses a mixed approach. In this embodiment, the individualknock 1400 and misfire information 1410 is used to calculate both knock1400 and misfire information 1410 for each cylinder. In addition, thecurrent knock 1400 and misfire information 1410 is input to the MBT PIcontroller 1440. Also, the current engine MBT criterion 1435 for thecurrent cylinder is used to control ignition timing, see FIG. 39.

[0246] The mixed MBT control method 1495 runs every combustion event.The knock 1450 and misfire limit 1460 managers select the knock andmisfire limits for the current cylinder and uses them for the PIsaturation using the knock processor 1408 and misfire processor 1418.However, the PI integrator is reset using the next cylinder's knock andmisfire limit. That is, if the output could be saturated by either theknock or misfire for the next cylinder, the integrator will be reset toits corresponding boundary value.

[0247] The MBT timing controller of the mixed method 1495 is similar tothe average approach method (compare FIGS. 38 and 39). Both the averageand the mixed methods use only one PI controller 1440. The difference isthat the average method uses a single knock manager 1450 and a singlemisfire manager 1460, while the mixed method uses multiple ones. Thus,the output timing limit signal 1480 has individual knock and misfirelimits. The advantage of using the mixed method is that only one PIcontroller 1440 is used for all cylinders which reduces the throughputrequirement. Also, use of multiple knock 1450 and misfire managers 1460produces improved fuel economy.

[0248] Section H: Closed-Loop Individual Cylinder Air/Fuel RatioBalancing

[0249] This feature pf the present invention comprises a method ofcontrolling individual cylinder air to fuel (A/F) ratios using a closedloop 1300 and an ionization signal 100. An individual cylinderionization signal 100 is used to calculate the minimum timing for besttorque (MBT) timing information of that cylinder. This MBT timinginformation 1320 is then used to control the individual cylinder's A/Fratio using a closed loop 1300. The control is based upon therelationship between the MBT timing information and the A/F ratio. Inaddition, an adaptive learning method is employed to modify (or update)the feedforward control logic block of the present invention.

[0250] The individual cylinder A/F ratio of an internal combustionengine 161 varies due to the fact that the intake manifold cannotdistribute airflow into the individual cylinders evenly, even when theglobal A/F ratio (i.e., the average A/F ratio of all the cylinders) ismaintained at stoich. The difference in A/F ratio between individualcylinders affects engine emission, fuel economy, idle stability, vehicleNoise, Vibration and Handling (NVH), etc.

[0251] The closed loop control of an individual cylinder's A/F ratio ofthe present invention utilizes the MBT criterion, see Section F: RobustMulti-Criteria MBT Timing Estimation Using Ionization Signal, providedby the ionization signal 100 or by the in-cylinder pressure signal, seeSection J: The Determination of MBT Timing Through the Net PressureAcceleration of the Combustion Process, to balance the A/F ratios of theindividual cylinders.

[0252] This invention is a subsystem of an ignition diagnostics andfeedback control system using ionization current feedback illustrated inFIG. 13. It is labeled 1300 in FIG. 13. When an engine 161 is operatednear to its MBT spark timing, it is known in the art that engine MBTtiming criterion, calculated from either in-cylinder pressure or from anionization signal 100, is a function of the A/F ratio that the engine161 is operated at. When the A/F ratio increases or moves to the leandirection (i.e., a leaner A/F ratio), the MBT spark timing is advancedand moves forward from Top Dead Center (TDC). This movement is due tothe fact that leaner the A/F ratio is, the longer it takes for thecombustion flame to develop. FIG. 40 shows a test relationship curve ofMBT spark timing versus A/F ratio using a 2.0 L, four cylinder enginerunning at 3000 RPM with Wide Open Throttle (WOT).

[0253] When the engine 161 is operated near the MBT spark timing, therelationship between A/F ratio and MBT spark timing information orcriterion (obtained using either the ionization signal 100 or thein-cylinder pressure signal) also holds at the individual cylinderlevel. For the same reasons discussed above, the MBT spark timing of arelatively lean cylinder (i.e., a cylinder operated at a lean A/F ratio)is advanced when compared with cylinders operated with relatively richA/F ratios.

[0254]FIG. 41 shows a test relationship of MBT timing information andA/F ratio for individual cylinders of a 2.0 L, four cylinder enginerunning at 1500 RPM, 2.62 Bar Brake Mean Effective Pressure BMEP with20% engine gas re-circulation (EGR) and ignition timing at 47° BeforeTop Dead Center BTDC. The engine 161 was run very close to stoich withan A/F ratio of 14.54. Furthermore, the relatively leanest cylinder(e.g., cylinder #4 with an A/F ratio of 14.96) had its MBT timingcriterion (a relative criterion indicating how far the current sparktiming of the cylinder is from MBT timing) 2 degrees more advanced thanthe mean MBT criteria. Similarly, the cylinder with the richest A/Fratio (cylinder #3 with an A/F ratio of 14.13) had its MBT timingcriterion 1 degree behind (or delayed when compared to) the mean MBTspark timing.

[0255]FIG. 41 has been redrawn in FIG. 42 to show the individualcylinder relationship of A/F ratio and MBT timing criteria. From FIG.42, it is seen that the relationship of A/F ratio versus MBT criteria isgenerally linear even though the data is collected from individualcylinders. From FIG. 42, it can be determined that a predominantlylinear relationship exists between MBT timing information and A/F ratioeven at the individual cylinder level when the engine is operated nearits MBT timing.

[0256] The present invention uses this relationship to balance the A/Fratio for individual cylinders. The method used in the present inventionuses a closed loop controller to adjust (or trim) the fuel of individualcylinders such that all cylinders have the same MBT timing criterion.Using the relationships illustrated in FIGS. 40 and 42, the A/F ratiosof the individual cylinders are balanced. FIG. 43 illustrates the closedloop control method of the present invention for balancing individualcylinder A/F ratios.

[0257] This control method consists of seven major logic blocks orsteps: a) calculating a mean MBT timing coefficient 1320, b) calculatingerror of unbalancing 1330, c) error integration of the individualcylinder difference 1340, d) feedforward fuel trim coefficient for eachindividual cylinder 1350, e) Rescale trim coefficient for eachindividual cylinder 1360, f) adaptive updating feedforward fuel trimcoefficient 1370, and g) individual cylinder final fueling coefficientcalculation 1380. The control method of the present invention balancesthe A/F ratio between the individual cylinders caused byengine-to-engine variations, uneven intake airflow due to intakemanifold geometry, and other related factors. This controller isdisabled when the engine is either knock and misfire limited. In apreferred embodiment, it is run once every engine cycle so that the MBTtiming information is updated for each cylinder.

[0258] The inputs to the present control method are the MBT timingcriterion obtained using the method described in Section F: RobustMulti-Criteria MBT Timing Estimation Using Ionization. The output fromthe closed loop control 1300 in the present invention is used as amultiplier of an individual cylinder fuel command to correct theindividual cylinder A/F ratios. The following is a description of eachof the seven functional blocks or steps or logic blocks of the closedloop 1300 of the present method and apparatus (see FIG. 44).

[0259] First, a mean MBT timing coefficient is calculated 1320. Theoutput of the MBT timing estimation method from either the in-cylinderpressure method or an estimate using an ionization signal 100 can berepresented as a vector with a size equal to the number of cylindersmeasured in units of Degree After Top Dead Center (DATDC). LetL_(MBT)(i) represent the MBT timing criterion obtained from the MBTtiming estimation in Section F, where index i represents the cylindernumber. The mean of the MBT timing criterion for all cylinders can becalculated using the following formula:

L _(MBT-MEAN)=1/nΣL _(MBT)(i),  (Equation 1)1320,

[0260] where n is the number of cylinders and L_(MBT)(i) is summed from1 to n.

[0261] Next, an error of unbalancing is calculated 1330. The error inthe MBT timing coefficient, i.e., the MBT timing coefficient errorL_(MBTERR)(i), caused by the unbalancing of the individual cylinders iscalculated by subtracting the mean of the MBT timing coefficientL_(MBTMEAN) from the MBT timing criterion L_(MBT)(i) as illustrated inthe following equation:

L _(MBTERR)(i)=L _(MBT)(i)−L _(MBT-MEAN), I=1, 2, . . . , n  (Equation2)1330.

[0262] Third, an error integration of the individual cylinder difference1340 is performed. The integration of the MBT timing error, i.e., theMBT timing coefficient integration error for an individual cylinder,ERR_(MBT)(k+1), can be calculated using the following equation:

ERR _(MBT)(k+1)=K ₁ *[ERR _(MBT)(k)+L _(MBTERR)(k)],  (Equation 3)1340,

[0263] where k is a time step index representing the k^(th) enginecycle, L_(MBTERR)(k) is the error vector from step b at the kth enginecycle, K₁ is the integration gain coefficient with a typical value of0.001 and can be used as a calibration coefficient for the closed loopcontrol method of the present invention.

[0264] Fourth, a feedforward fuel trim coefficient for each individualcylinder 1350 is calculated. The feedforward fuel trim coefficientvector FT_(FDD) (each element represents a corresponding individualcylinder) is the output of a look-up table 1352. It is a function ofengine speed and load. Due to the intake manifold geometry, theindividual cylinder unbalancing changes as the airflow rate changes. Thelook-up table 1352 is used to compensate for this variation. Thecombined fuel trim coefficient is called the raw fuel trim coefficientFT_(RAW) and is calculated by adding the integration of the MBT timingerror, ERR_(MBT), and the feedforward fuel trim coefficient, FT_(FDD)1350. See Equation 4 below:

FT _(RAW) =ERR _(MBT) +FT _(FDD),  (Equation 4)1350.

[0265] Note that when the engine 161 is operated with abnormalcombustion conditions (such as knock, misfire/partial-burn, etc.), theMBT timing criterion will not be used for an A/F ratio balancingcalculation due to unreliable MBT timing estimation 1353 and in thiscase the integrated value will not be updated. Consequently, the rawfuel trim coefficient FT_(RAW) is set to the feedforward fuel trimcoefficient FT_(FDD) 1354.

[0266]FIG. 45 is an example of the look-up table 1352 which is stored inmemory 112. The memory can be RAM, ROM or one of many other forms ofmemory means. Engine speed is mapped along the vertical axis from 650rpm (e.g., idle) to 6500 rpm (e.g., rated rpm) in 12 increments. Thenormalized engine load is mapped along the horizontal axis from 0 to 1,in 10 increments. Thus, the 12×10 data parameter matrix has valuesstored for the feedforward fuel trim coefficient vector FT_(FDD) foreach combination of engine speed and engine load. Normally, this table1352 is obtained through the engine calibration process.

[0267] Fifth, the trim coefficient for each individual cylinder isrescaled 1360. The raw fuel trim coefficient FT_(RAW) does not have tomeet the constraint that the summation of vector FT_(RAW) equals thenumber of cylinders such that overall fuel flow rate is unchanged. Thefollowing rescaling operation 1360 takes care of this in which the rawfuel trim coefficient FT_(RAW) is rescaled yielding the rescale trimcoefficient FT_(SCALED):

FT _(SCALED)(k)=(n*FT _(RAW)(k))/(ΣFT _(RAW)(k)),  (Equation 5)1360,

[0268] where index k represents the kth cylinder, n is the number ofcylinders and FT_(RAW)(k) is summed from 1 to n. That is, the rescaledtrim coefficient FT_(SCALED) is calculated by multiplying the raw fueltrim coefficient FT_(RAW) by the number of cylinders in the engine 161,and then dividing this total by the sum of all the raw fuel trimcoefficients FT_(RAW) for each cylinder in the engine 1360.

[0269] With the help of this step, the fuel flow for a given enginecycle will be the same as the commanded one. However, it isredistributed so as to balance the individual cylinders. To ensure afailsafe operation, saturations (i.e., upper and lower bounds) areapplied to the fuel trims for individual cylinders 1362. Let FT_(UP) andFT_(LOW) represent the upper and lower bound vectors for a fuel trimvector. Both FT_(UP) and FT_(LOW) are calibration coefficients.Normally, the upper and lower saturation vectors FT_(UP) and FT_(LOW)are set in such a way that there is enough freedom to balance the A/Fratio for all cylinders with reasonable variation range. Typical valuesof FT_(UP) and FT_(LOW) are 0.9 and 1.1 which can compensate a 10percent A/F ratio variation. If any element of FT_(SCALED) is outside ofthe upper or the lower bound, it will be reset to its boundary value,and the associated unsaturated elements will be rescaled 1364, using theprocess similar to (Equation 5) so that the mean of the trim vector isequal to the number of cylinders in the engine 161. The saturated fueltrim vector is called the final trim vector FT_(FINAL).

[0270] After the final fuel trim vector FT_(FINAL) is calculated byresealing the unsaturated elements of FT_(SCALED) 1364, the individualcylinder error integrator for the (k+1)^(th) engine cycle ERR_(MBT)(k+1)will be reset 1366 to reflect the scaling and saturation operation. Itis calculated by subtracting the feedforward fuel trim coefficientFT_(FDD) from the final fuel trim vector FT_(FINAL) and then dividingthis total by the integration gain coefficient K₁. See equation 6 below:

ERR _(MBT)(k+1)=[FT _(FINAL)(k+1)−FT _(FFD)(k+1)]/K ₁,  (Equation6)1366.

[0271] This resetting of the individual cylinder error integratorERR_(MBT)(k+1) 1366 works to prevent overflow and typical integratorwinding problems.

[0272] In the sixth step, the feedforward fuel trim coefficient isadaptively updated 1370. In a preferred embodiment, the adaptive portionof the closed loop control method modifies or updates the feedforwardlook-up table 1352 based upon the current engine operating conditions1372 (engine speed and load). When the engine 161 is operated in aneighborhood of the lookup table mesh point, the adaptive algorithmupdates the new mesh point value FTM by

FTM _(NEW)(k)=FTM _(OLD)(k)+ERR _(MBT)(k),

[0273] where k is the engine cycle number and both FTM_(NEW)(k) andFTM_(OLD)(k) represents the updated and current mesh point value. Thegoal is that when the A/F ratio for all the cylinders are balanced, thefeedforward output provides the final fuel trim coefficient.

[0274] In the seventh step, the individual cylinder final fuelingcoefficient is calculated 1380. The final fueling (FUEL_(FINAL)) commandfor each individual cylinder is calculated by multiplying the commandedfueling or fueling command (FUEL_(CMD)) and the final fuel trimcoefficient FT_(FINAL) of a corresponding cylinder as shown in thefollowing equation:

FUEL _(FINAL)(i)140=FUEL _(CMD) *FT _(FINAL)(i), i=1, 2, . . . ,n.  (Equation 7)1380.

[0275] In a preferred embodiment, the steps (or instructions) in FIG. 43are stored in software or firmware 107 located in memory 111 (see FIG.46 which is a logic block diagram of the air to fuel ratio controlsystem of the present invention). The steps are executed by a controller121. The memory 111 can be located on the controller 121 or separatefrom the controller 121. The memory 111 can be RAM, ROM or one of manyother forms of memory means. The controller 121 can be a processor, amicroprocessor or one of many other forms of digital or analogprocessing means. In a preferred embodiment, the controller is enginecontrol unit ECU 121.

[0276] The ECU 121 receives an ionization signal 100 from an ionizationdetection circuit 10. The ECU 121 executes the instructions 107 storedin memory 111 to determine a desired air to fuel ratio AFR for eachcylinder. It then outputs the desired fuel command 975 to some form offuel control mechanism such as a fuel injector 151 located on the engine161.

[0277] Section I: Exhaust Gas Control Using a Spark Plug IonizationSignal

[0278] Exhaust gas re-circulation (EGR) is an effective way to reduceNOx emissions in an internal combustion engine 161. The external exhaustgas recirculation EGR widely used in the prior art is calibrated usingengine mapping points. That is, the desired exhaust gas re-circulationEGR rates used in controlling an engine are mapped to various engineoperating conditions such as load and speed. Note that the amount of EGRaffects the engine emission and also its combustion stability. Tomaximize the NOx emission reduction without fuel economy penalty, it isdesired to have high EGR rate, but on the other hand, too much EGR maydestabilize the engine combustion process. Therefore, in some cases itis desired to have as much EGR as possible with stable combustion. Dueto engine to engine variation, engine aging, and engine operationalenvironmental variation, open-loop calibration of a desired EGR rate isvery conservative. In the present invention, a closed loop controller isused to regulate the external exhaust gas re-circulation EGR to maximizefuel economy and minimize emissions. In another preferred embodiment,the internal exhaust gas re-circulation EGR is controlled by the closedloop 1600.

[0279] Exhaust gas re-circulation EGR is used to reduce flametemperature and slow down the combustion process. Because of this, it isnot used when the engine is operated with a light load or at idleconditions. Exhaust gas re-circulation EGR finds its greatest benefitwhen used in partial load conditions, where the pumping loss is reducedby a relatively wider throttle opening. The combustion process alsobenefits from a wider throttle opening.

[0280] At a wide open throttle, where the pumping loss is at its minimumand the torque output is the priority, the exhaust gas re-circulationEGR is not used anymore. As stated earlier, open loop control of exhaustgas re-circulation EGR uses extensive engine calibration efforts to seta desired exhaust gas re-circulation EGR rate at various partial loadconditions. Due to the exhaust gas re-circulation EGR and the sparktiming open loop control, the desired exhaust gas re-circulation EGR isusually too conservative to fully take advantage of the exhaust gasre-circulation EGR fuel economy benefit. In addition, the exhaust gasre-circulation EGR rate 1610 is typically controlled by the exhaust gasre-circulation EGR valve position 1620. As the engine 161 ages, theexhaust gas re-circulation EGR valve and its plumbing are clogged by theexhaust deposits and the true exhaust gas re-circulation EGR deliveredto the cylinders could be changed dramatically.

[0281] This feature of the present invention uses the ionization signal100 and closed loop control 1600 of the exhaust gas re-circulation EGRto provide the engine 161 with either the minimum spark timing for besttorque (MBT) timing or knock limited timing to yield the maximum fueleconomy benefits associated with exhaust gas re-circulation EGR.

[0282] The purpose of exhaust gas re-circulation EGR is to 1) reduce NOxemission and to 2) improve internal combustion engine 161 fuel economywith a given NOx emission level. The formation of NOx depends on twofactors: First, there must be enough oxygen to oxidize the N₂, and theother is there must be a high enough temperature for the NOx formationreaction to accelerate. When exhaust gas re-circulation EGR is inducedinto the combustion chamber, the exhaust gas will act like an inert gasand absorb the heat from the combustion reaction. As a result, the globegas temperature, the temperature at which combustion takes place, isreduced through the EGR dilution effect. The reduced temperature slowsdown the NO_(x) formation. The suppressive effect of EGR on theformation of NO_(x) is enhanced as the volume of the re-circulatedexhaust gas relative to the volume of fresh air admitted into the engineis increased, i.e., the EGR rate is increased.

[0283] When exhaust gas re-circulation EGR is used in the engine 161,less fresh air enters the combustion chamber due to hot exhaust gastaking up more volume in the chamber. Thus, the air/fuel mixture becomesdiluted because there is less room for oxygen in the cylinder (i.e., thedilution effect). In order to meet the same load requirement, thethrottle opening has to be increased to compensate the increase ofintake manifold pressure due to the exhaust gas re-circulation, andtherefore to maintain the same air flow (or oxygen). The increasedthrottle opening not only reduces the pumping loss, but also acceleratesthe combustion process due to stronger turbulence resulting from theincrement of the intake manifold pressure.

[0284] Although the addition of exhaust gas re-circulation EGR reducesthe combustion speed because of the dilution effect in the cylinder, thehigher turbulence balances it out to an extent. The result of the twoeffects is that the exhaust gas re-circulation EGR dilution slows downthe combustion gradually as the EGR rate 1610 increases. At the pointwhen too much exhaust gas re-circulation EGR is added to the combustionchamber, the combustion becomes unstable. Thus, the employment of highEGR rates tends to cause instability of the engine operation.Consequently, the EGR rate should be controlled to maintain a balancebetween suppression of NOx emission and engine combustion stability.

[0285] One of the measures of combustion stability is the COVariance(COV) of Indicated Mean Effective Pressure (IMEP) since it increases asthe combustion goes unstable. In order to have the best fuel economypossible, the control strategy is to add as much exhaust gasre-circulation EGR to the combustion chamber as possible withoutdeteriorating the combustion quality. In the prior art, the calculationof the IMEP COV uses an in-cylinder pressure signal. However, it isdifficult for production engines to measure combustion stability due tolack of in-cylinder pressure sensors which are production ready, have alow price, and are reliable. This invention proposes to use theionization signal 100 to generate a combustion stability criterion anduse this criterion to maximize the exhaust gas re-circulation EGR rate1610 and thereby maximize fuel economy at a given emission allowance.

[0286] As the exhaust gas re-circulation EGR rate 1610 increases, thecombustion uses earlier spark timing to accommodate the longercombustion duration for the best fuel economy, or in other words, to runthe engine at its Minimum timing for the Best Torque (MBT). When thespark timing is not knock-limited, the minimum time for the best torqueMBT spark timing increases as the exhaust gas re-circulation EGR rate1610 goes up. Meanwhile, the combustion instability gradually increasesdue to the requirement for a longer burn duration. Typically, when 0-90%of the burn duration takes more than 70 crank angle degrees, thecombustion tends to become unstable and is usually no longer acceptable.At this point, fuel consumption starts to increase due to thedeteriorated combustion process. Also, the hydrocarbon (HC) emissiongoes up rapidly due to unburned fuel if more exhaust gas re-circulationEGR is used. This instability limit is reached when the minimum time forbest torque MBT timing is advanced beyond a certain crank degrees BeforeTop Dead Center (BTDC) with a typical value of 40 degrees. To preventthis from happening, the engine exhaust gas re-circulation EGR rate 1610is calibrated so that the minimum time for best torque MBT timing isless than a calibratable value such as 40 degrees BTDC. A disadvantageof this approach is that the calibration is very conservative due to thefact that the actual exhaust gas re-circulation EGR rate 1610 varies dueto engine aging, etc.

[0287] The proposed closed loop maximum exhaust gas re-circulation EGRrate controller 1600 utilizes the relationship between the engineminimum time for best torque MBT timing and COV of IMEP (see FIG. 47).Generally, when the COV of IMEP is used as a combustion instabilityindicator, less than 3% is considered as a good combustion. As shown inFIG. 47, when more exhaust gas re-circulation EGR is added to thecylinders, the COV of IMEP increases as the minimum time for best torqueMBT timing increases. When the COV of IMEP is greater than 3%, the MBTtiming is about 43 degrees BTDC and the exhaust gas re-circulation EGRrate 1610 is about 20%.

[0288] In the present invention, the minimum best time for best torqueMBT spark timing is used, instead of COV of IMEP, as a measure for themaximum dilution rate (exhaust gas re-circulation EGR rate 1610)control. FIG. 47 illustrates the correlation between COV of IMEP and theminimum time for best torque MBT spark timing for a 2.0 L, 4 cylinderengine running at 1500 RPM with 2.62 Bar BMEP.

[0289] When exhaust gas re-circulation EGR is added to the cylinder, theinitial temperature of the unburned mixture increases because of the hotexhaust gas. The unburned mixture is more prone to auto-ignite when theinitial temperature is higher and causes the engine to knock. The engineminimum best time for best torque MBT spark timing might not be knocklimited without the addition of exhaust gas re-circulation EGR. However,as the exhaust gas re-circulation EGR rate increases, the engine sparktiming may become knock limited. Furthermore, if more exhaust gasre-circulation EGR is added, the mixed gas becomes hotter and the knockbecomes more severe. As a result, the spark timing is backed off fromthe MBT timing to avoid the knocking. This leads to bad fuel economy.

[0290] On the other side, an increased exhaust gas re-circulation EGRrate reduces the engine pumping loss. Therefore, the preferred oroptimal exhaust gas re-circulation rate EGR 1606 for best fuel economyis an exhaust gas re-circulation EGR rate which is a little higher thanthe knock limited exhaust gas re-circulation rate EGR 1608. See FIG. 48.Since a direct EGR rate measurement is not preferable due to its highcost, the present invention calculates a preferred knock limited sparktiming by using MBT timing criteria generated from an ionization signal100. When the engine is knock limited by exhaust gas re-circulation EGR,the engine is not run at its minimum best time for best torque MBT sparktiming 1612. Instead, the engine is run at a retarded (or delayed) sparktiming which is retard from the MBT spark timing. The amount of delay isreferred to as the “MBT offset” 1614, and is quantified by the MBTtiming criterion (see FIG. 48). The exhaust gas re-circulation rate EGRis reduced to the knock limited spark timing.

[0291] In summary, a determination is made as to whether the engine 161is knock limited (1603) (See FIG. 50). When the exhaust gasre-circulation EGR rate is not knock limited, the engine 161 sets itsexhaust gas re-circulation rate EGR 1610 to an optimal exhaust gasre-circulation rate EGR 1606 such that the engine 161 runs at theexhaust gas re-circulation minimum best time for best torque sparktiming limit (or EGR MBT timing limit) (1607). When the exhaust gasre-circulation EGR rate is knock limited, the engine 161 sets itsexhaust gas re-circulation EGR rate to a knock limited EGR rate 1608 atwhich the engine 161 runs at a retarded MBT spark timing limit (1609).The engine 161 uses a calibratable MBT timing criterion to determine theretarded MBT spark timing limit. The difference between the retarded MBTspark timing limit and the EGR MBT timing limit is called the MBT offset1614.

[0292] As part of the ionization feedback control system (see SectionC), FIG. 49 shows a logic block diagram of the closed loop EGR ratecontrol 1600 that maximizes the dilution rate. The EGR closed loopcontroller 1600 works with the closed loop MBT timing controller 1430,1490, 1495 (see Section I). The controller 1600 has five inputs andseven logic blocks, or logic devices. The controller 1600 output is theEGR valve command 1630. A functional description of each of the fiveinput signals, engine speed (RPM) 135, engine load 1060, knock limitflag 1404, MBT timing signal 1480, and MBT criterion error 1438 islisted below:

[0293] The current engine speed 135 measured in RPM (Revolutions PerMinute) is the filtered engine speed representing the steady stateengine speed. The engine load information 1060 is calculated as apercentage of maximum load, fueling or the Indicated Mean EffectivePressure (IMEP). The knock limit flag 1404 is obtained from the closedloop MBT timing controller 1430, 1490, 1495 (See Section G, Closed LoopMBT Timing Control Using Ionization Feedback). The knock limit manager1450 senses when the engine 161 is operated in knock limit mode wheneither the knock flag 1404 and the knock intensity 1402 are in the knockor the non-audible knock state. The MBT timing input signal 1480 is alsoobtained from the closed loop MBT timing controller 1430, 1490, 1495(see Section G). When the absolute value of the MBT criterion 1435 error1438 is less than a calibratable value, the current ignition timing isconsidered at the MBT timing. The MBT timing used in this controller1600 is a filtered one. The MBT criterion error 1438 is the controllererror of the closed loop MBT timing controller 1430, 1490, 1495.Individual cylinder MBT timing criterion 1435 is calculated from anionization signal 100 or in-cylinder pressure signal generated using aparameter estimation method (see Sections F, J). This parameterdiscloses whether the current engine spark is before or behind the MBTspark timing 1612 for that individual cylinder. The criterion error 1438is filtered to remove the combustion-to-combustion variation factor.

[0294] The functionality of each of the logic blocks (or logic devices),the EGR MBT limit table 1640, the proportional and integral (PI) gainand error generator 1650, the proportional and integral (PI) controller1660, the feedforward EGR rate table 1670, the adaptive learning EGRrate adapter 1680, the saturation manager 1690, and the EGR valvemetering controller 1695 is discussed below:

[0295] The EGR MBT limit table 1640 is a logic block that functions as alook-up table which uses engine speed 135 and engine load 1060 as itsinputs. It can be stored in RAM memory, ROM memory, tape, a CD, or anyof a number of digital or analog memory storage devices. Each individualpoint on the look-up table can be calibrated by mapping the EGR rate1610 to a specific engine speed 135 and load 1060 condition (see step1700 in FIG. 51a). It provides (or outputs) to the PI gain and errorgenerator 1650 a recommended EGR MBT timing limit signal 1642 which iscorrelated to a combustion stability criterion such as COV of IMEP(1710). With a desired combustion stability criterion (such as COV ofIMEP is less than 2.5%), a MBT timing limit can be determined.

[0296] In a preferred embodiment, the PI gain and error generator 1650can be a processor, microprocessor or any form of processing means. Thislogic device can operate in two different engine states, knock limitedor not knock limited. The knock limit flag input 1404 is used todetermine which of the two states that the PI gain and error generatoroperates at (1720), a) the knock limited state, or b) the not knocklimited state. The PI gain and error generator 1650 output signal 1652comprises both of the PI controller 1660 gains (proportional andintegral) PI_gain and the PI controller 1660 input error PI_error. Theproportional gain is set to zero at all times.

[0297] In the knock limited state, the PI gain (PI_gain) and error(PI_error) are generated using the MBT criterion error 1438 inputsignal. The first step is to determine if the MBT criterion error 1438is less than a calibratable retard MBT timing limit (1730) such as 3crank degrees. If the criterion error 1438 is less than a calibratableretard MBT timing limit, then the spark timing is below the offset fromMBT timing. Consequently, the exhaust re-circulation rate EGR can beincreased until it reaches the knock limited EGR 1608 (see FIG. 48).

[0298] Thus, if the MBT criterion error 1438 is less than a calibratableretard MBT timing limit (that is, a higher EGR is needed), the PI error(PI_error) is set to one and the integral gain of PI_gain is set to acalibratable value (1732) such as 0.1 The result is that the PI controloutput 1662 increases to increase the EGR.

[0299] If the MBT criterion error 1438 is greater than or equal to acalibratable retard MBT timing limit, then the spark timing is above theoffset from MBT timing. The exhaust re-circulation rate EGR should bereduced until the spark timing is at the offset MBT timing, or EGR MBTtiming. Consequently, the exhaust re-circulation rate EGR can be reduceduntil it reaches the knock limited EGR 1608 (see FIG. 48)

[0300] Thus, if the MBT criterion error 1438 is greater than acalibratable retard MBT timing limit (that is, a lower EGR is needed),the PI_error is set to negative one and the integral gain of PI_gain isset to a calibratable value (1734). The result is that the PI controloutput 1662 decreases to reduce the EGR rate 1610.

[0301] In the not knock limited state, the PI gain and error outputsignal 1652 is generated using the MBT ignition timing signal 1480 fromthe MBT timing controller 1440, 1490, 1495. The first step is todetermine if the MBT ignition timing signal 480 is less than the EGR MBTspark limit (1735). If the MBT timing is less than the EGR MBT sparklimit, PI_error is set to one and the integral gain of PI_gain is set toa calibratable value. As a result, the PI control output 1662 increasesto increase the EGR rate 1610 until it reaches an optimal exhaust gasre-circulation EGR rate 1606. If the MBT ignition timing signal 1480 isgreater than or equal to the EGR MBT limit, PI_error is set to negativeone and the integral gain of PI gain is set to a calibratable value(1739). As a result, the PI control output 1662 decreases the EGR rate1610 until it reaches the optimal exhaust gas re-circulation EGR rate1606.

[0302] In a preferred embodiment, the proportional and integral (PI)controller 1660 can be a controller, a processor, microprocessor or anyform of controller or processing means. As stated above, the PIcontroller 1660 receives as an input the PI gain and error generator1650 output signal 1652 which comprises both of the PI controller 1660gains (proportional and integral) PI gain and the PI controller 1660input error PI_error (1740). The PI controller 1660 output 1662 is thesum of the proportional and the integral control outputs. Theproportional control output is calculated by taking the product of thePI_error and the proportional gain (1742). The integral control outputis calculated by taking the product of the integral gain and theintegration of the PI error (1744).

[0303] A novel feature of this controller is that the integrated valuewill be reset if the combined output (feedforward and PI outputs) issaturated. When this condition occurs, the PI integrated value is set toa value such that the combined output equals the saturated value (seebelow) to avoid overflow and rewinding.

[0304] The feedforward EGR rate table 1670 is a function of engine speed135 and load 1060. This table 1670 can be initially obtained by mappingthe engine maximum EGR rate 1610 with a satisfactory combustionstability criterion (such as COV of IMEP) 1750 (see FIG. 51b). Theaccuracy of this mapping process can be corrected by the adaptivelearning process controller 1680 (see below). It can be stored in RAMmemory, ROM memory, tape, a CD, or any of a number of digital or analogmemory storage devices. The table 1670 outputs a feedforward EGR rate1672 (1752) which is added to the output 1662 of the PI controller 1660by summer 1663 to produce a desired EGR rate signal 1664 (1754).

[0305] As mentioned above, the adaptive learning EGR rate adapter 1680compares the final desired EGR rate 1664 with a default EGR rategenerated from the current engine 161 operating conditions (i.e., givenengine speed 135 and load 1060) which serve as inputs to the adaptivelearning device 1680 (1756). (Thus, in one preferred embodiment, theadaptive learning apparatus 1680 comprises a processor and acomparator). It will generate a correction value signal 1682 for thefeedforward table 1670 (1758). If the engine 161 runs at the currentoperational condition for a calibratable period, the updated value 1682at that operating condition is sent to the feedforward table 1670 toadaptively correct values in the table 1670. The adaptive learningapparatus 1680 together with the Feedforward EGR rate table 1670constitute the feedback portion of the loop 1600.

[0306] The saturation manager 1690 is a logic device which imposes anupper and a lower bound for the maximum desired EGR rate 1610 that isallowed. The integral output of PI controller output 1662 will be resetif the combined output signal 1664 (feedforward 1672 and PI outputs1662) is saturated (1760), i.e., the desired exhaust gas re-circulationEGR rate exceeds either the upper or lower bounds. When this conditionoccurs, the PI integrated value is set to a value such that the combinedoutput equals the saturated value 1692. The lower limit is normallyzero, and the upper limit is dependant upon a number of factors such asEGR valve maximum opening, exhaust and intake manifold pressuredifference, etc. The upper limit can also be a function of the engine's161 operating conditions.

[0307] The EGR valve metering controller 1695 converts the desired EGRrate 1664 into a desired valve opening 1620 by outputting EGR valvecommand 1630 (1764). Due to the closed loop control, the accuracyrequired for this conversion is much less than with conventional openloop EGR rate control.

[0308] Section J: The Determination of MBT Timing Through the NetPressure Acceleration of the Combustion Process

[0309] The determination of MBT timing (the minimum spark timing for thebest torque) at various engine-operating conditions requires extensivemapping efforts. The existing cylinder pressure sensor based controlschemes developed for MBT timing control, such as peak pressurelocation, 50% mass fractions burned location, and pressure ratiomanagement, are still based on pressure signal observation and stillneed certain calibration efforts.

[0310] This invention intends to use the maximum acceleration rate ofthe net pressure increase resulted from the combustion in the cylinderto control the spark timing. When the maximum acceleration point of thenet pressure lines up with the top dead center (TDC), the MBT timing isachieved. The invention will not only simplified the spark timingcontrol scheme, but also make the MBT timing search much reliable.

[0311] The MBT timing is also called the minimum spark timing for thebest torque or the spark timing for the maximum braking torque. Unlessthe spark timing at a certain engine operating condition is limited byknock or is delayed intentionally for a specific condition, there alwaysexists the best spark timing where the same amount of air/fuel mixturecan yield the maximum work. For an ideal combustion cycle, a combustionprocess happens instantaneously, when the ignition, flame kerneldevelopment, flame propagation all occur at the same time. The TDC isthe location that the ideal combustion occurs. In reality, combustioncannot finish instantaneously. The MBT timing is the result of constantchanging of combustion chamber volume due to piston moving and thenon-idealistic combustion process.

[0312] Traditionally, the search of MBT timing is done through sparksweep. Unless requested by operating condition for delayed spark timing,almost every calibration point needs a spark sweep to see if the enginecan be operated at the MBT timing condition. If not, certain degree ofsafety margin is needed for the condition to avoid pre-ignition orknock. The open loop spark mapping usually requires tremendous effort toachieve a satisfactory calibration.

[0313] In recent years, various close loop spark timing control schemeshave been proposed based on cylinder pressure measurements or sparkionization sensing. Based on massive testing data observation, it wasfound that the peak pressure usually occurs around 15 degree ATDC at MBTtiming; the 50% mass fraction burned mostly happens between 7 to 9degree ATDC at MBT timing. The algorithm published in prior art SAE2000-01-0932 controls PRM (pressure ratio management) around 0.55 toobtain the MBT timing. Since the criteria are based on observations andmay change at different operating conditions, each algorithm still needscertain extent of calibration effort. It is clear that the combustionprocess has to be matched with the engine cylinder volume change toattain the best torque. However, there is no sound theory to support whypeak pressure has to occur around 15 degree ATDC, or why 50% burned hasto happen around 8 degree ATDC, or why PRM should be around 0.55 for theMBT timing conditions.

[0314] A combustion process is not strictly a chemical process. In fact,it is a chemical process as well as a physical process and is usuallydescribed by mass fraction burned versus crank angle. The mass fractionburned not only signifies how much chemical energy is released at eachcrank angle during the combustion, but also how fast the chemical energyis released. It has a characteristic S-shape and changes from zero toone from the beginning to the end of combustion. FIG. 52 shows the massfraction burned and its first and second derivatives. The firstderivation of MFB can be treated as the rate of heat release or thevelocity of the combustion process; while the second derivative can betreated as the acceleration of the combustion process. After the sparkdischarge, the flame kernel starts to form. Once the flame kernelbecomes stable, it develops very fast and the combustion process reachesits maximum acceleration point. Then the rapid burning period starts andreaches its maximum heat release velocity, and then the combustionprocess is slowed down and the attain its maximum deceleration point.Since the combustion cannot complete instantaneously and the chambervolume is constantly changing, where to align these critical pointsversus crank angle may have significant impact on how much useful workcan be accomplished during the combustion process. If we ignite themixture too soon, the pressure increase due to the heat release beforethe TDC would generate a negative work. If we don't ignite the mixtureon time, the heat release process would not be efficient enough toutilize the small volume advantages right at or slightly after the TDC.Therefore, where to ignite the combustion mixture becomes critical thatbest torque can be reached at certain spark timing.

[0315] The mass fraction burned is mostly determined by the well-knownRassweiler-Withrow method established in 1938 through pressuremeasurement. It uses the chamber volume at the ignition as a referenceand calculates the net pressure increase at every crank angle for thewhole combustion process, then normalizes the pressure by the maximumpressure increase toward the end of combustion. The procedure ignoresthe heat loss and mixture leakage during the combustion. Each percentageof pressure increase signifies the percentage of mass fraction of fuelburned at the corresponding crank angle.

[0316] Instead of using the mass fraction burned, we will use the netpressure change and its first and second derivatives to represent thedistance, velocity and acceleration of the combustion process. The netpressure is derived as follows:

[0317] At every crank angle after the ignition, the pressure P(i+1)compared to previous crank angle P(i), the difference is composed of twoparts. One part of the pressure change due to volume change can be foundthrough the difference between the P(i)*(V(i)/V(I+1))^(1.3)−P(i),assuming the pressure undergoes isentropic compression or expansion.Then the pressure difference resulted from combustion between these twocrank angle is P(i+1)−P(i)*(V(i)/V(i+1))^(1.3). This difference is stillevaluated at volume V(i). If we want to know the net pressure withoutany volume change since the ignition, the difference will again becompare with the volume at the ignition point as if the combustionundergoes constant volume combustion. Then the net pressure changebetween two crank angles is:

dP(i)=(P(i+1)−P(i)*(V(i)/V(i+1))^(1.3))*V(i)/V _(ig).

[0318] Finally, the net pressure at each crank angle will be:

P _(net)(i)=P _(net)(i−1)+dP(i),

[0319] where P is pressure, V is volume and V_(ig) is the chamber volumeat the ignition point. After the net pressure is found for the wholecombustion process. Its first and second derivatives can be treated asthe velocity and acceleration of the net pressure, which can be alsoused to signify as the velocity and the acceleration of the combustionprocess (Shown in FIG. 53). Once the air/fuel ratio and EGR rate aredetermined, the peak velocity and the peak acceleration of thecombustion process do not change with spark timing very much. The wholecombustion process is like a distance runner who is entering a race.Where to attain his maximum acceleration and where to reach the peakvelocity determine how well the final result is. As we know, the workgenerated before the top dead center (TDC) is wasted to fight with themoving piston and produce heat. However, it is a necessary step for theflame to establish itself for further flame development. The useful workis done after the TDC. From FIGS. 52 and 53, we can see that thecombustion process reaches its maximum acceleration point at arelatively early stage, which indicates that the early flame preparationis finished at this point. If we achieve this maximum acceleration pointbefore TDC, some of the rapid burning period will be wasted before theTDC. If we attain the maximum acceleration point after the TDC, therapid burning period right after the maximum acceleration point willoccur at a bigger cylinder volume that results lower combustionefficiency. Therefore, it is reasonable to start the rapid burningperiod right at the top dead center, which allows that the most usefulwork to be generated most efficiently. In other words, when the sparktiming is advanced to the point where the maximum acceleration pointlining up with the top dead center, we can obtain the most useful workout of the combustion process and we can achieve the MBT timing.

[0320]FIG. 54 shows the torque value at different spark timing for 2500rpm, 7.86 bar (114 psi) BMEP and FIG. 55 shows the corresponding netpressure acceleration curves at different spark timing. It is clear fromFIG. 54 that the MBT timing is at 28 degree BTDC. The peak accelerationpoints showing in FIG. 55 gradually advance as the spark timing isadvanced. At 28 degree BTDC, the peak acceleration of pressure islocated close to the TDC.

[0321] The tests conducted at various engine operating condition hasalso proved that the maximum acceleration point locating at TDC is wherewe achieve the MBT timing. This rule applies to the combustion processwith one peak heat release curve, such as PFI (port fuel injection)engines, natural gas engines, and GDI (gasoline direct injection)engines with only one time fuel injection in the cylinder.

[0322] While the invention has been disclosed in this patent applicationby reference to the details of preferred embodiments of the invention,it is to be understood that the disclosure is intended in anillustrative rather than in a limiting sense, as it is contemplated thatmodification will readily occur to those skilled in the art, within thespirit of the invention and the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A method of controlling engine ignition timing,comprising: using estimated MBT timing criterion and ignitiondiagnostics to control the engine ignition timing.
 2. The method ofcontrolling engine ignition timing according to claim 1 wherein saidignition diagnostics comprises knock and misfire information.
 3. Themethod of controlling engine ignition timing according to claim 2wherein said step of using estimated MBT timing criterion and ignitiondiagnostics to control engine ignition timing, comprises the followingsteps: calculating said MBT timing criterion, said knock information andsaid misfire information; generating an error signal by comparing saidMBT criterion with a reference signal; outputting said error signal to acontroller; producing a proportional error signal by multiplying saiderror signal by a proportional gain; producing an integrated errorsignal by integrating said error signal with an integral gain; resettingsaid integrated error signal if an engine is knock or misfire limited;outputting a feedforward signal; and outputting a timing signal bysumming said proportional error signal, said integrated error signal andsaid feedforward signal.
 4. The method of controlling engine ignitiontiming according to claim 3 further comprising the steps of: modifyingopen loop MBT timing over an engine operation map; and compensating saidengine for engine-to-engine variations.
 5. The method of controllingengine ignition timing according to claim 3 wherein said integratederror signal is reset by a knock limit manager if said engine is knocklimited.
 6. The method of controlling engine ignition timing accordingto claim 3 wherein said integrated error signal is reset by a misfirelimit manager if said engine is misfire limited.
 7. The method ofcontrolling engine ignition timing according to claim 3 wherein eachcylinder is controlled individually and wherein said MBT timingcriteria, said knock information and said misfire information iscalculated for each cylinder.
 8. The method of controlling engineignition timing according to claim 3 wherein the engine ignition timingis controlled using an averaged approach, comprising the step of:controlling all cylinders globally by using a single MBT timing controlparameter, worst case knock information and worst case misfireinformation.
 9. The method of controlling engine ignition timingaccording to claim 3 wherein the engine ignition timing is controlledusing a mixed approach, comprising the steps of: using one MBT timingcontrol parameter for all cylinders; using individual cylinder knockinformation; and using individual cylinder misfire information.
 10. Themethod of controlling engine ignition timing according to claim 3wherein said integrated error signal is reset by a knock limit managerif said engine is knock limited and wherein said integrated error signalis reset by a misfire limit manager if said engine is misfire limited.11. The method of controlling engine ignition timing according to claim5 further comprising the steps of: moving an advance limit signal in anadvance direction when there is no knock; leaving said advance limitsignal unchanged when there is a inaudible knock; and moving saidadvance limit signal in the retard direction when said engine isknocking.
 12. The method of controlling engine ignition timing accordingto claim 6 further comprising the steps of: moving a retard limit signalin a retard direction when said engine is not at partial burn; movingsaid retard limit signal in an advance direction when said engine is atpartial burn; and moving said retard limit signal in an advancedirection by adding a correction when said engine misfires.
 13. Themethod of controlling engine ignition timing according to claim 10further comprising the steps of: moving an advance limit signal in anadvance direction when there is no knock; leaving said advance limitsignal unchanged when there is a inaudible knock; moving said advancelimit signal in the retard direction when said engine is knocking;moving a retard limit signal in a retard direction when said engine isnot at partial burn; moving said retard limit signal in an advancedirection when said engine is at partial burn; and moving said retardlimit signal in an advance direction by adding a correction when saidengine misfires.
 14. A closed loop MBT timing controller, comprising: aproportional and integral controller; a knock limit manager operablyconnected to said proportional and integral controller; a misfire limitmanager operably connected to said proportional and integral controller;and a saturation manager operably connected to said proportional andintegral controller.
 15. The closed loop MBT timing controller accordingto claim 14 wherein said proportional and integral controller comprises:a proportional controller; an integral controller operably connected tosaid proportional controller; a feedforward controller operablyconnected to said proportional controller; and a reset manager operablyconnected to said integral controller.
 16. The closed loop MBT timingcontroller according to claim 14 further comprising: a plurality of saidknock limit manager, wherein each of said plurality of knock limitmanagers corresponds to one of a plurality of cylinders; a plurality ofsaid misfire limit manager, wherein each of said plurality of knocklimit managers corresponds to one of said plurality of cylinders; and aplurality of said proportional and integral controller, wherein each ofsaid proportional and integral controllers corresponds to one of saidplurality of cylinders.
 17. The closed loop MBT timing controlleraccording to claim 14 further comprising: a plurality of said knocklimit manager, wherein each of said plurality of knock limit managercorresponds to one of a plurality of cylinders; a plurality of saidmisfire limit manager, wherein each of said plurality of knock limitmanagers corresponds to one of said plurality of cylinders; and whereinsaid proportional and integral controller controls all of said pluralityof cylinders.
 18. The closed loop MBT timing controller according toclaim 14 wherein said closed loop MBT timing controller comprises asingle proportional and integral controller, a single knock limitmanager, and a single misfire limit manager; and wherein said singleproportional and integral controller uses a single MBT timing controlparameter, said knock limit manager uses worst case knock informationand said misfire limit manager uses worst case misfire information,whereby all cylinders are controlled globally.
 19. The closed loop MBTtiming controller according to claim 15 wherein said proportional andintegral controller further comprises an adaptive learning controlleroperably connected to said feedforward controller.
 20. The closed loopMBT timing controller according to claim 15 further comprising: aplurality of said knock limit manager, wherein each of said plurality ofknock limit managers corresponds to one of a plurality of cylinders; aplurality of said misfire limit manager, wherein each of said pluralityof knock limit managers corresponds to one of said plurality ofcylinders; and a plurality of said proportional and integral controller,wherein each of said proportional and integral controllers correspondsto one of said plurality of cylinders.